This study analyzes the effect of one-child policy on marriage market in China, and focuses on leftover situation, marriage age, and the age differential between husband and wife. Taking age of 30 as a cut-off point, the one-child policy has increased the leftover proportion about 1.2%, with 1.8% on men and 0.6% on women. Although the problem of urban leftover women has made eye-catching of the general public, the problem of the leftover men is much more serious than that of women: with the former arising from the true over-supply of men while the latter due to the matching process. The one-child policy on marriage age is positive and significant, no matter for urban, rural residents, or migrants, but the effect is smaller in the urban area, which is consistent with the fact that the sex ratio is more balanced in urban area. This policy also increases the age differential between husband and wife on the whole; however, it is positive and significant for the male-head families but negative for the female-headed families.