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Based on the TRACE-P emission data and a Shanghai local emission inventory, the regional air quality model Models-3/CMAQ was applied with the mesoscale model MM5 to simulate the distribution and transport status of O3 and PM10 in the Yangtze River Delta (YRD) in January and July 2001. Ten days' hourly monitoring data at Shanghai monitoring sites were used to verify the model performance. Results show that the correlation coefficients between monitoring and simulation data of O3 and PM10 are 0.77 and 0.52, and the indices of agreement reach 0.81 and 0.99, respectively. The Models-3 simulation shows a 27% underestimation of the maximum O3 hourly concentration, but performs well in average O3 hourly concentration simulation with a normalized bias of -3.1%. The model shows a 10% underestimation of the average PM10 hourly concentration, with a normalized bias of 46%. Models-3/CMAQ has the ability to simulate the processes of air pollution transport in the YRD, and the model results are acceptable. Among the 16 major cities of the YRD, the maximum O3 hourly concentrations in 14 cities exceed the class II Chinese National Ambient Air Quality Standard (CNAAQS). The high O3 concentration area covers most of the south Jiangsu and north Zhejiang Province. Influenced by local emissions and northerly air pollution transport, the daily average concentrations in Taizhou, Yangzhou, Nanjing, Zhenjiang and Changzhou cities during January of 2001 exceed the Class II national standard. Air pollution transport and chemical transformation are quite obvious in the YRD. In summer, under strong radiation conditions, the air pollutants emitted from southern cities usually impose a negative impact on the downwind cities, due to secondary pollution formation; while under weak radiation conditions, the pollutants impact the surrounding area with primary pollution. In winter, the particle pollution level in the YRD is relatively high, which is closely related to the transportation of particulates from the north area to the YRD. The air pollution in the YRD has developed as a regional problem, rather than just a local one.