Abstract: To study the effects of silicon on the chlorophyll fluorescence characteristics of photosystem Ⅱ (PSⅡ)in tobacco leaves under cadmium stress, an indoor hydroponic experiment was conducted to analyze the characteristics of fast chlorophyll fluorescence induction dynamics of PSⅡ in cv. Yunyan87. The results showed that the fast chlorophyll fluorescence induction dynamics curve (OJIP) changed under cadmium stress, and both the minimum fluorescence value(F_o) and maximum fluorescence value (F_m) significantly decreased. Under cadmium stress, the maximum photochemical efficiency (F_v/F_m), oxygen evolution complex (OEC), receptor library capacity (S_m), quantum yield for electron transport (φ_Eo), density of reaction centers (RC/CS_o) and performance index (PI_abs) decreased. While the relative variable fluorescence at K-step (V_k), the relative variable fluorescence at J-step (V_J) and approximated initial slope of the fluorescence transient (M_o) significantly increased. These data indicated that cadmium stress damaged tobacco leaf's photosynthetic integrity, altered the quantity of per PSⅡ reaction centers and the harmfulness to donor-and acceptor-side of PSⅡ and inhibited photosynthetic electron transmission. The fluorescence kinetic curves of Cd_0.05+Si and Cd_0.10+Si treatments coincided with that of the control. OEC, S_m, φ_Eo, RC/CS_o and PI_abs were significantly increased, while V_k, V_J and M_o significantly decreased. Therefore, Cd_0.05+Si and Cd_0.10+Si treatments stabilized the structure and function of PSⅡ, alleviated cadmium damage to photosynthesis of tobacco leaves and was beneficial to photosynthetic electron transport.