The implementation of the comprehensive two-child policy is a major adjustment of China's fertility policy, which is of great significance to study the impact of the implementation of this policy on labor supply. This study uses data of population census of 2010, and sets a plan for possible changes in the fertility level after the implementation of the comprehensive two-child policy across China. On this basis, the impact of the implementation of the comprehensive two-child policy on China's future labor supply scale is measured. The results show that our country's future labor supply will show a trend of slow decline before 2030, whereas after which a trend of rapid decline regardless of whether the birth policy is adjusted. The implementation of the comprehensive two-child policy, to a certain extent, has increased the scale of labor supply after 2030, and has played a positive role in slowing down the rapid decline in labor. However, the overall trend cannot be reversed. Therefore, further adjustments to future fertility policies should take into account of other socio-economic factors, e.g. population structure, old-age security, and women's willingness to bear children of childbearing age.