[Objective] The effects of straw returning and nitrogen fertilizer application on weed density, quantity, community structure, soil nutrients rice yield and components, were analyzed through a long-term field experiment of fertilization and straw returning in Hanzhong Basin in order to study the eco-economic effects of straw returning and nitrogen fertilizer application in paddy field under different rotation patterns. [Method] Field experiments included four treatments under two different rotation patterns; conventional fertilization NPK + without straw return(CNS/CK), conventional fertilization NPK(CSM) + straw return, and conventional fertilization with PK, N reduced by 15% (CSM1) + straw returning, PK, N reduced by 30% (CSM2). The species, quantity and density of weeds in rice field were investigated during rice maturity. After rice harvest, soil nutrient content in 0-20 cm soil sample, rice yield and yield components were determined. [Result] The amount of nitrogen fertilizer and straw returning had great effects on weed species and quantity, the number and species decreased in different degrees, and there was significant difference in weed density among the treatments. The total weed densities of RCSM, RCSM1, and RCSM2 were 27.79%, 34.5% and 8.06% lower than those of RCNS (CK) under rape-rice rotation, respectively. Compared with RCNS (CK), WCSM, WCSM1 and WCSM2 decreased the total weed density by 14.59%, 36.51% and 11.7% under rape-rice rotation, respectively. Compared with CK, the density of Echinochloa crusgalli (L.) Beauv. of the other three treatments had no significant difference. The weeds family of Gramineae and Cyperaceae decreased in different degrees, and the weeds family of Onagraceae and Scrophulariaceae increased significantly. Compared with the CK, the pH of CSM, CSM1, and CSM2, decreased in different degrees, and the difference of CSM1, was significant. Compared with CK, RCSM, RCSM1, and RCSM2, increased the available K by 14. 46%, 8.72% and 9.41%, and the available P by 44.05%, 31.1% and 32.75% under rape-rice rotation, respectively. Organic carbon of RCSM1, significantly increased by 20.35%, while no significant difference was found in other treatments. Under wheat-rice rotation, available K, available P and organic carbon were significantly increased compared with the CK, available P was increased by 41.01%, 20.6% and 12.63% by WCSM, WCSM1, and WCSM2, respectively, and available K increased by 45.89%, 24. 24%, 19. 14%, and soil organic carbon increased by 16. 18%, 14. 23% and 10.86%, respectively. WCSM had the biggest increase in the various indicators. Compared with CK, RCSM and RCSM1, significantly increased rice yield by 5.97% and 7. 68% under rape-rice rotation, respectively. WCSM1, significantly increased rice yield compared with CK, growth was 4.92% under wheat-rice rotation. Under rape-rice, panicle length, effective panicle, grain number per panicle, seed setting rate and 1000-grain weight of RCSM1, were higher than those of other treatments, except that the increase of effective panicle was lower than that of RCSM. Compared with CK, RCSM1, increased by 8. 13%, 1.51%, 26.3%, 2.09% and 4.24%, respectively. Under wheatrice rotation, panicle length, effective panicle and seed setting rate of WCSM were higher than that of other treatments, and grain number per panicle and 1000-grain weight of WCSM1, were higher than that of other treatments. [Conclusion] Straw returning was beneficial to the accumulation of soil nutrients, such as available P, available K and organic carbon, and to the reduction of the number and species of weeds, the improvement of weed community structure and the reduction of grass damage risk under the two rotation patterns. The components of rice yield could be increased to achieve the effect of stable yield and yield increase under the condition of 15% reduction of nitrogen fertilizer. Therefore, it is possible to control the growth of dominant weeds and improve the weed community structure by returning straw. The efficiency of nitrogen fertilizer utilization and maintaining the soil fertility could be improved by reducing the amount of nitrogen fertilizer reasonably. The potential environmental pollution of farmland caused by pesticide could be reduced to achieve stability and increase the yield. [ABSTRACT FROM AUTHOR]