Flesh firmness is an important quality attribute of watermelon, more and more producers and consumers pay attention to this. In this study, the BC7F1 population was constructed using PI271769 (known to have different characters compared to the recurrent parent) as a donor parent, and the elite watermelon cultivar 203Z as the recurrent parent, and we found that some watermelon of BC7F1 population have hard flesh. One hundred eighty five simple sequence repeat (SSR) markers on 11 chromosomes were used to detect polymorphism between PI271769 , 203Z,soft flesh pool and hard flesh pool. BVWS00954 on chromosome 6 of them was found to have polymorphism between soft flesh pool and hard flesh pool. Then we found that BVWS00954 was linked with flesh firmness in the BC7F2 segregating population through one – way ANOVA, and this correspond with different watermelon germplasm. These results laid an important foundation for fine mapping, map-based cloning and marker-assisted selection breeding of watermelon flesh firmness gene .