The resistane heredity of Ridgegourd downy mildew was studied by a diallel cross arnong six culivare. The results showed that both general companing ability and specifil companing ability were important to resistance; the heredity of resistance could be explained by the additive dominative genehcal model. The ratio of dominant gene by recessive alleles, heritability in narrow sense was 69. 63%. The least number of additive gene was 4.