Abstract: Genetic analysis of resistance for anti-source 4G21 to Didymella bryoniae（Auersw.）on Cucumis melo L. was studied，using six generation population F1，F3，BCs、BCr and parents from a cross between a resistant variety 4G21（C. var. chinensis）and a susceptible variety 3A832（C. melo var. saccherinus）. The results showed that：Resistance level of population F1 was slightly lower than that of parent 4G21，it illustrated that disease resistance gene represented as incomplete dominant gene in generation population F1. The segregation ratio of resistant-susceptible was 1:1 in BCs，and 3:1 in F3 genealogy. The results implied that disease resistance was governed by a single incomplete dominant gene，named as Sb-x，it was located on linkage group LG1 of molecular map on melon，and closely linked with both sides of the SRAP marker loci of me45em42-4，me45em2-3，me45em2-4 and me3em42-4，me3em42-3，the genetic distances were 2 cM and 3 cM respectively.

Key words: Cucumis melo L., Didymella bryoniae, disease resistance gene, molecular location