Abstract: VRTN gene is the major gene affecting the number of thoracic vertebra in pigs, which QQ genotype (ins/ins) individuals have one double ribs more than qq (-/-) genotype ones. The molecular marker-assisted selection method of VRTN gene in two landrace pig populations was explored to improve the number of ribs of mating pigs. In the study, PCR were used to detect the distribution of VRTN genes in 420 commercial pigs of Wens Group and 2 specialized landrace pigs (913 W51 Landrace and 240 W52 Landrace), which affected thoracic vertebra number (rib number). It is verified that QQ type had nearly one pair of ribs more than qq type in Wens terminal pigs by effect analysis of commercial pork pigs, which indicated that gene improvement could be carried out through molecular marker-assisted selection. The allele frequencies of VRTN gene in the W51, W52 Landrace populations were not significantly different, and the favorable allele frequencies were 0.844 and 0.905 respectively. Through the correlation analysis between genotype and phenotypes of breeding traits, it was found that among W51 Landrace pigs, the dominant genotype had obvious body length advantage and had no influence on other breeding traits. In W52 line, the dominant allele had a significant negative correlation with the estimated breeding value of age at 100 kg/115 kg body weight, but had no significant correlation with other traits. The effect of VRTN dominant allele type was consistent with the breeding goal. Molecular marker-assisted selection could be carried out for W51 and W52 lines both. Combining with field practice breeding, W51 achieved 100% complete purification of dominant allele frequency after half a year through population renewal and optimization. W52 was basically purified after 2 years while expanding its population.