Brassinosteroids (BRs) are a kind of hormone widely distributed in a variety of plants. Brassinosteroid Insensitive 1 (BRI1) is the main signal receptor of BR signaling pathway, which plays a crucial role in plant growth and development and stress response. In this study, we used tomato varieties Micro-Tom (MT) and SlBRI1 overexpression plants (Atrd29A:SlBRI1) as experimental materials to investigate the effects of low temperature on photosynthetic characteristics, chlorophyll fluorescence parameters and cold resistance genes, in order to reveal the response of SlBRI1 gene driven by Atrd29A promoter to low temperature stress. The results showed that: (1) Low temperature stress increased the expression of SlBRI1 in MT plants, while the expression of SlBRI1 in Atrd29A:SlBRI1 plants were higher than that of MT plants. Low temperature stress for 5 days resulted in wilting of all plants, and Atrd29A:SlBRI1 plants wilted less and recovered better. (2) The net photosynthetic rate (Pn), stomatal conductance (Gs), transpiration rate (Tr), maximum photochemical efficiency of PSII (Fv/Fm), actual photochemical efficiency (ΦPSII), light capture efficiency (Fv ''/Fm'') and photochemical fluorescence quenching coefficient (qP) of all tomato seedlings were significantly decreased under low temperature stress. On the 5th day of low temperature stress, these indexes of SlBRI1 overexpressing plants were significantly higher than those of MT plants. Meanwhile, the intercellular CO2 concentration (Ci) of SlBRI1 overexpression lines was significantly lower than that of MT. (3) The expression levels of transgenic plants SlICE1、SlCBF1、SlCBF3 and SlDRCI7 were significantly increased under the same condition, and the expression levels of SlICE1、SlCBF1、SlCBF3 and SlDRCI7 in SlBRI1 transgenic plants after low temperature treatment were significantly higher than those in MT plants. The results indicated that the expression of SlBRI1 induced by Atrd29A could improve the expression of SlBRI1, alleviate the effects of low temperature stress on plant photosynthesis and chlorophyll fluorescence parameters, and enhance the cold resistance of tomato plants.