Potting seedling of cassava cultivar SC8 was used as materials to investigate the changes of leave chlorophyll content, chlorophyll fluorescence parameters and the expressions of proteins in PSⅡof cassava seedlings exposed to low temperature (5 ℃) for 7 days. The results show that during the stress, chlorophyll a and chlorophyll b contents were both decreased first and then slowly increased, reaching the minimum 2 days after stress; maximum photochemical efficiency (Fv/Fm), photochemical quantum efficiency of photosystemⅡ(ΦPSII), photochemical quenching (qP), non-photochemical quenching (NPQ) and electron transport rate (ETR ) were significantly decreased with Fv/Fm continuously declined, while ΦPSII, qP and ETR first decreased to minimum level 2 days after stress, and then slowly rose, and NPQ decreased to minimum level 5 days after stress. The significant decrease of chlorophyll content and chlorophyll fluorescence parameters indicate that the light-harvesting ability, openness and photochemical conversion rate in PSII reaction center were decreased significantly, which inhibiting the photosynthetic efficiency of cassava leaves. The expression level of D1, D2, OEC and Rubisco reached the lowest 2 days after stress with D1 decreased significantly. The down-regulation of the expression of proteins in PSⅡverifies at protein level that low temperature inhibits photosynthesis of leaves.