Taking day temperature of 25 ℃ and night temperature of 20 ℃ as the control group， variations of photosynthetic carbon assimilation related indexes of wild type and hta9hta11 double mutant of Lycopersicon esculentum Mill. in treatment group （day temperature of 15 ℃ and night temperature of 10 ℃） were compared. The results show that chlorophyll content in hta9hta11 double mutant in treatment group is slightly lower than that of wild type； its net photosynthetic rate， contents of sucrose and starch， activities of fructose-1，6-bisphosphate aldolase and fructose-1，6-bisphosphatase， and relative expression levels of TK， GAPDH， SBPase， PRK， RbcL， RCA， FBPase and FBA genes are significantly lower than those of wild type； while its ribulose-1，5-bisphosphate carboxylase／oxygenase activity and relative expression level of RbcS gene are significantly higher than those of wild type. It is suggested that photosynthetic carbon assimilation ability of hta9hta11 double mutant of L. esculentum is lower than that of wild type under mild hypothermia condition， and histone variant H2A.Z may play an important role in regulating photosynthetic carbon assimilation pathway of L. esculentum.