Abstract: To improve the screening efficiency of near-isogenic lines（NILs） of Chinese cabbage resistant to clubroot disease by molecular marker-assisted selection, The clubroot-resistant material G 57 was used as the donor parent, and the susceptible material H 227 with excellent traits was used as the recurrent parent.By using the method of foreground and background selection of molecular markers, we studied the number of population screened by molecular markers and the initial generation of recurrent parental background selection, and several important factors affecting the screening efficiency were also explored.The results showed that when the sample size of each backcross population was 18,the screening efficiency of target single plant was the best, and background screening from BC₂F₁ generation had the highest probability of obtaining ideal single plant and the lowest coefficient of variation within the population under the same sample size.Through the analysis of the genetic recovery rate of the plant, the efficient molecular breeding technology system suitable for clubroot was explored, which accelerated the construction process of near-isogenic lines of resistance to clubroot in Chinese cabbage.