Under the action of low level microwave electromagnetic field of 300MHz,the changes of chlorophyll fluorescence dynamics process and photosynthetic pigment in leaf of spinach and tobaccoare are different.When the fluorescence dynamics parameters F_0 and F_ VI /F_V of spinach decrease,ΔF_V/T and F_V/F_m increase. The fluorescence dynamics parameter F_0 of tobacco increases,while ΔF_V/T and F_V/F_m decrease. There is a difference between photosynthetic pigment of spinach and tobacco. The content of chlorophyll in leaf of spinach and tobacco decrease,but the content of carotenoid in leaf of spinach increase. These results show that low level microwave electromagnetic field leads to the decrease of potential active of reaction center PSⅡand the photochemical efficiency of PSⅡ in leaf of tobacco.Spinach can keep the photosynthesis in leaf through the change of heterogeneity of PSⅡand the increases of carotenoid.