In order to understand the effects and mechanism of the drought resistance of uniconazole on Zinnia seedlings growth,the photosynthetic characteristics and leaf anatomical structure were studied of Zinnia,‘Fangfei 1’ using uniconazole under water stress.The results showed that:(1)Under water stress,the growth of Zinnia was inhibited at different degrees,chlorophyll content was decreased significantly,photosynthesis was inhibited,some changes were occurred in leaf structure.(2)Under different water stress,uniconazole could reduce the plant height,increase the stem diameter,leaf area,leaf thickness.Palisade tissue thickness,rootshoot ratio and chlorophyll content increased significantly.The net photosynthetic rate(P_n),transpiration rate(T_r),and stomatal conductance(G_s) and water use efficiency (WUE) were improved.The results suggested that uniconazole could strengthen the drought resistance of Zinnia seedling,the decline of P_n was considered as a result of stomatal restriction under light and moderate water stress,but nonstomatal restriction under severe water stress.