Effects of freezing pretreatment factors, including moisture content, freezing time and freezing temperature, on bulking degree and uniformity of Pinus sylvestris wood treated by microwave were investigated. The results showed that suitable moisture content of freezing pretreatment was 20%. When moisture content of the wood was over fiber saturation point, bulking degree was increased with rising of moisture content while bulking uniformity was decreased. Increasing freezing time had no remarkable effect on bulking uniformity but could enhance bulking degree. Freezing temperature at – 20℃ could get better bulking uniformity.