The pathway genes play an essential role in shoot apical meristem maintenance and floral organ development, and under intense selection during crop domestication. The carpel number is an important fruit trait that affects fruit shape, size and internal quality in cucumber, but the molecular mechanism remains elusive. Here, we found that expression was negatively correlated with carpel number in cucumber cultivars. led to increased number of petals and carpels, whereas overexpression of resulted in more sepals, petals and carpels, suggesting that and function as a negative and a positive regulator for carpel number variation, respectively. Biochemical analyses indicated that CsWUS directly bound to the promoter of and activated its expression. Overexpression of , a - MADS-box gene, resulted in more petals and carpels. CsFUL1 can directly bind to the promoter to stimulate its expression. Furthermore, we found that auxin participated in carpel number variation in cucumber through interaction of CsARF14 with CsWUS. Therefore, we have identified a gene regulatory pathway involving , , and in determining carpel number variation in an important vegetable crop - cucumber.