Abstract: Abstract: Tomato plants (Solanum lycopersicum cv. Jinguan5) were grown in a climate chamber to determine the responses of tomato quality attributes to the difference between day and night temperatures (DIF). Six day/night temperature combinations 31/19, 28/22, 25/25, 24/12, 21/15, and 18/18℃ with respective DIFS of 12, 6, 0, 12, 6, 0 at 25, and 18℃ mean daily temperature were observed. The dynamic change of soluble sugar and sucrose content, dry mass portioning in different organs, free amino acid and soluble protein, and fruit quality of tomatoes were measured. At the daily average temperature of 18℃, the soluble sugar and sucrose content in fruits were highest under 12℃ DIF treatment, and lowest under 0 DIF treatment; while at the daily average temperature of 25℃, the soluble sugar and sucrose content in fruits were highest under 6℃ DIF treatment. At the daily average temperature of 18℃, the total free amino acids and soluble protein content of leaves were highest under 12℃ DIF treatment, and lowest under 0 DIF treatment; while at the daily average temperature of 25℃, the total free amino acids of leaves were highest under 6℃ DIF treatment, and soluble proteins were also to be the maximum under 6℃ DIF treatment in young fruit and picking time. The dry mass allocation proportions in fruits at the daily average temperature of 18 and 25℃ were both the maximum under 6℃DIF treatment, and minimum under 12℃ DIF treatment. The organic acid content of fruits at the daily average temperature of 18℃ was lowest under 12℃ DIF treatment, while at the daily average temperature of 25℃, the content was lowest under 6℃ DIF treatment. VC, soluble proteins, and lycopene of fruits have the opposite trend compared with the organic acid content at the daily temperature of 18℃. Studies suggested that under the condition of a daily average temperature of 18℃ with DIF from 0-12℃, the greater the DIF was, the more soluble sugar and sucrose were accumulated in the fruits, the larger free amino acids and soluble protein were, and the better fruit quality was. It's good for dry mass transportation to increase DIF appropriately, but too high or too low a DIF was not conducive to the dry mass accumulation in fruits. Under the condition of a daily average temperature of 25℃with DIF from 0-12℃, the interior fruit quality under 6℃ DIF was the best. It was concluded that under the different daily temperature within the same DIF treatments, the interior fruit interior quality under 25℃ treatment was better than that under 18℃