Abstract:GRAS transcription factor is one of the most important transcription factors for plants in regulating growth and abiotic stress response. However, there have no research about GRAS regulating high temperature stress. In order to further explore the functions of SlGRAS4 gene in tomato, we used heat resistant tomato LA2093 as the test material, identified the gene structure, promoter sequence and evolutionary relationship of SlGRAS4 gene, detected the expression level of SlGRAS4 gene upon abiotic stress and hormone treatments by qRTPCR, analyzed the function of SlGRAS4 gene responding to hightemperature by VIGS. The results showed that: (1) bioinformatics analysis showed that the length of SlGRAS4 protein was 666 amino acids, with 75 737.72 Da molecular weight and 6.31 isoelectric point, the typical domain of the GRAS family was specifically detected at the Cterminal between 277-657 aa in SlGRAS4 protein; the elements related to abscisic acid and salicylic acid responding were detected in promoter region of SlGRAS4 gene; evolutionary relationship analysis showed SlGRAS4 protein has the nearest relationship with Nicotiana tabacum NTGRAS1 protein, and predicted SlGRAS4 has similar biological functions with its homologous genes. (2) The expression of SlGRAS4 gene in tomato increased to the highest and upregulated 8.86, 4.86, 55.38 and 7.63 folds compared with the control after 12 h of high temperature, low temperature, salt and drought stress treatments, respectively; as well as reached the peak value after 8 h of ABA and SA treatments, which upregulated 120.72 and 3.55 folds compared with the control, respectively, indicating that SlGRAS4 may be involved in a variety of abiotic stress responses and hormone signal transduction. (3) Under high temperature stress, SlGRAS4silencing tomato plants (VSlGRAS4) were wither than the control plants (Ve), and Fv/Fm, SOD and POD activities were significantly reduced, and contents of REL and H2O2 were significantly increased, indicating that silencing SlGRAS4 aggravated oxidative damage of the cell membrane, and reduced photosynthetic capacity, and weakened activity of ROS scavenging enzyme in tomato plants. (4) qRTPCR analysis showed that the expression level of HsfA1b (high temperature signal response gene), ZAT10 and ZAT12 (ROS signaling response genes), CuZnSOD, FeSOD, APX1, APX2 and CAT (ROS scavenging enzyme code genes) were also significantly downregulated in VSlGRAS4 plants. The results indicated that SlGRAS4 can enhance heat tolerance of tomato through hightemperature and ROS signal transduction. The studies showed the expression of SlGRAS4 gene was significantly induced under high temperature, low temperature, drought, salt, ABA and SA, and the heat tolerance of tomato was reduced after silencing SlGRAS4 gene, indicating tomato SlGRAS4 gene has heat resistance function, and this will lay a foundation for further analysis of heat molecular mechanism.