In order to explore the effects of day and night temperature difference on tomato growth and development, a controlled experiment with tomato cv. ‘Jinguan 5’ was conducted in an artificial climate chamber (TPG1260, Australia) from July to December, 2012. The daily average temperature was designed at 18 ℃, and the day/night temperatures were designed at 18/18 ℃ (0 ℃ difference), 21/15 ℃ (6 ℃ difference), and 24/12 ℃ (12 ℃ difference), with the effects of these day and night temperature differences on the photosynthesis pigment contents, photosynthesis characteristics, and fluorescence kinetic parameters at seedling stage, flowering stage, young fruit stage, and maturity stage studied. With the increasing temperature difference, the chlorophyll (Chla and Chlb) contents increased gradually, but the Chla/Chlb ratio decreased. The chlorophyll content at 12 ℃ difference increased significantly, as compared with that at 0 ℃ difference. At the same temperature differences, the photosynthesis pigment contents showed a decreasing trend with tomato growth. During the whole growth period of tomato, the leaf P_max, A_max, A_q, and C_e reached the highest at 6 ℃ difference, followed by at 0 ℃ difference, and the lowest at 12 ℃ difference. The maximum photochemical efficiency (F_v/F_m), photochemical quenching, and electron transport rate were the maximum at the 6 ℃ difference, and the lowest at the 0 ℃ difference. At the daily average temperature 18 ℃, a 6 ℃ difference could effectively promote the leaf photosynthesis of tomato, being conducive to the tomato growth.