The processing tomato variety Jinfan 3166 was used to study the effects of synergistic regulation of brackish water with different salinity and nitrogen application rate on photosynthetic characteristics and yield of processing tomatoes under mulched drip irrigation to rationally develop and utilize brackish water resources in arid areas. Nine treatments of irrigation mineralization levels including 1.0 g/L （S1）， 3.0 g/L （S2）， 5.0 g/L （S3） and nitrogen application rates including 180 kg/hm² （N1）， 240 kg/hm² （N2）， and 300 kg/hm² （N3） were set up. The results showed that the SPAD value， transpiration rate （T_r）， net photosynthetic rate （P_n）， stomatal conductance （G_s） and yield of leaves in processing tomato decreased gradually with the increase of irrigation salinity at the same nitrogen application level， and the leaf water use efficiency （LWUE） increased significantly at the stage of mature. The increase in nitrogen application （N3） significantly increased the SPAD value， T_r， P_n， and G_s of leaf at the levels of S1 and S2. The N2 treatment at the S3 level had the best promotion effect， and the yield increased by 11.46%， 8.69%， and 5.17% compared to the N1 treatment， respectively. There was no significant difference in the yield of processing tomatoes under the N3 treatment at the levels of S1 and S2. It can be concluded that a salinity of 3.0 g/L irrigation and a nitrogen application rate of 300 kg/hm² can promote the photosynthesis of processing tomatoes and ensure the yield of processing tomatoes taking into account the photosynthetic characteristics and yield changes of processing tomatoes under mulched drip irrigation.