To understand the effect of freeze-thaw processes on organic nitrogen conversion in forest soil, the upper layer and lower layer of soil in three types of forest in the temperate zone (hardwood broad-leaved forest, Korean pine broad-leaved forest, and secondary birch forest in the Changbai Mountains) were selected to study the dynamic changes in microbial biomass and soil available nitrogen after indoor freeze-thaw experiments (-15-5℃). The contents of soil microbial biomass carbon (SMBC) and the soil microbial biomass nitrogen (SMBN) in the upper soil layer of three forests were, in most cases, higher than in the control treatment (soil incubated at 5℃ for 4 days; recorded as CK) during the freeze-thaw period. The SMBC and SMBN in the upper soil layer of the three forest types were significantly higher than those in the lower soil layer (P < 0.05) subjected to freeze-thaw cycles and showed no obvious spatial heterogeneity. The effect of the freeze-thaw process on the content of NO₃^--N in soil was not clear. There was no significant difference (P > 0.05) in the soil NO₃^--N content between different freeze-thaw cycles at the same layer in each forest type. The NH₄⁺-N content of the upper soil layer in three forest types showed similar trends with the frequency of freeze-thaw cycles, with obvious NH₄⁺-N release characteristics in the third, fourth, and fifth freeze-thaw cycles. The responses of nitrogen mineralization (nitrification) in the three forest soils to the freeze-thaw process were clear. The temperature of the freeze-thaw, the frequency of the freeze-thaw cycles, and soil layer significantly affected the net nitrification rate and the net nitrogen mineralization rate. The net nitrification rate of the three forest soils fluctuated greatly. The net nitrification rate peaked in the upper layer after the second freeze-thaw cycle, followed by the seventh and the fifth freeze-thaw cycles. The soil net nitrification rate and net nitrogen mineralization rate in the upper layer of the three types of forests reached a peak for short-term freeze-thaw cycles and then followed a decreasing trend.