We investigated the effect of freezing and thawing on soil active organic carbon by collecting soil from natural Larix gmelinii-sedge wetlands in the Xiaoxing'an Mountains and Larix gmelinii wetlands after drainage afforestation in 2003, 1992, and 1985. The results indicated that there were significant differences in four kinds of soil organic carbon (SOC) content (P < 0.05), but with increased freezing and thawing times, the SOC content was basically unchanged. After 1, 2, 4, and 9 freeze-thaw cycles, the SOC content change was 1.64%, 9.68%, 2.32%, and 2.17%, respectively, under a -5-5℃ freeze-thaw treatment. But the chang was 2.55%, 6.45%, 3.00%, and 2.36%, respectively under a -25-5℃ freeze-thaw treatment, which indicated that the effect of the freeze-thaw action on SOC in soil was not obvious in the short term. Before and after freezing and thawing, the change in LFOC/SOC in four kinds of wetland soil was not obvious (P > 0.05), but with the increase in the number of freezing and thawing cycles, LFOC content declined at first and then increased, and the content was slightly higher than that in the control group after nine freeze-thaw cycles. DOC peaked after one freeze-thaw cycle, and the DOC content was 323.45, 278.21, 235.68, and 180.53 mg/kg, respectively, under a -5-5℃ freeze-thaw treatment. They were 314.75, 256.93, 238.25, and 204.44 mg/kg, respectively, under a -25-5℃ freeze-thaw treatment. In addition, the MBC/SOC change in the soil was not observed significantly before and after freezing and thawing (P > 0.05), but overall, the increase in drainage afforestation time increased the differences in MBC/SOC.