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In view of gas production rate being affected by solid content (TS) in the manure/stalk co-digestion, the bench-scale tests were carried out of mixed anaerobic co-digestion with raw materials containing complementary carbon and nitrogen for the purpose of evaluating the gas production characteristics of whole sweet-sorghum stalks and dairy manure. The co-digestion was at medium temperature ((37±0.5) °C) with a 1:1 ratio of sweet-sorghum stalks to dairy manure volatile solids (VS) in the substrate, and with four treatment groups of dairy manure samples of different solid contents, i.e., 2% (Group T2), 4% (Group T4), 6% (Group T6) and 8% (Group T8), methanogenic performances were analyzed, and the modified Gompertz model was used for dynamical analysis. Consequently, the tests showed that Group T2, among others, generated cumulative gas of 633.49 mL/(g VS) and cumulative methane of 350.26 mL/(g VS): the greatest of all the groups; in addition, the increase of TS would lead to decreasing of cumulative gas production rate, and obviously, high TS was not conducive to biogas production. The model fitting of modified Gompertz resulted in the correlation co-efficient (R² = 0.988 to 0.999). With an increase of TS, the delay period lengthened, and the maximum rate of methane production declined. Compared with other treatment groups, Group T2 was the best in terms of mixed digestion system. The concentration of COD and volatile fatty acids increased with the increase of TS. Summarily, it is expected that the achievment of the tests is of guiding significance regarding the efficient methane production and stability control of digestion process of mixed digestion of whole sweet sorghum stalks and dairy manure. [ABSTRACT FROM AUTHOR]