The genetic diversity of 78 self-incompatible lines of non-heading Chinese cabbage collected in the author’s laboratory was analyzed and the natural high temperature in summer in Wuhan was used to measure the heat injury indexes in order to screen nonheading Chinese cabbage varieties suitable for production under high temperature conditions in summer and to provide germplasm for breeding new heat-tolerant non-heading Chinese cabbage varieties. The results showed that Siji’aijiaotebaigengnaibaicai（Accession No. C72) had the lowest heat injury index among all the lines studied and its plants showed strong tolerance to high temperature. Compared with other lines,C72 had a higher enzymatic activity of both POD and SOD,lower content of malondialdehyde and lower relative conductivity,further indicating that C72 has stronger heat tolerance. It will provide a theoretical basis and germplasm for discovering and screening heat-tolerant non-heading cabbage resources in the Yangtze River Basin in summer,and guarantee the whole-year supply of non-heading Chinese cabbage in the Yangtze River Basin in China in summer.