Changes in gene expression in hybrids are closely related to the heterosis formation. Currently, few reports have been reported on key genes that promote the yield advantage formation in Chinese cabbage hybrid. In the present study, RNA sequencing and virus-induced gene silencing were performed to elucidate the underlying mechanisms of yield advantage formation in Chinese cabbage hybrid (weichunbai No.3). In total, 3652 and 2768 genes were differentially expressed genes between the Chinese cabbage hybrid and its parents in the rosette and the mature stages, respectively. These differentially expressed genes among the hybrid and its parents showed diverse expression patterns, and the overwhelming majority of differentially expressed genes were additively expressed genes. A vital additively expressed gene related to the plant weight, BraA09g035160.3C, was found by the weighted gene co-expression network analysis. Through virus-induced gene silencing technology, the expression level of BraA09g035160.3C in the hybrid was dramatically decreased, which resulted in slowing the hybrid growth, indicating that this gene could be related to the formation of hybrid yield advantage. These results will provide an important reference for in-depth research on the molecular mechanism underlying the yield advantage formation of Chinese cabbage hybrid.