In order to expand the application range of fast-growing wood, the poplar wood was impregnated with urea-formaldehyde resin, and the impregnated wood and non-impregnated (untreated) wood were treated with heat treatment. The microstructure, moisture absorption, water absorption and shrinkage performance of untreated, impregnated, impregnated combined heat-treated and heat-treated poplar wood were analyzed. The results showed that the resin filled in the vessels, wood fibers, wood rays, pits and the cell corner, and even inflated the cell wall after impregnation modification. The distribution of resin changed after heat treatment. The resin attached to the cell wall of impregnated combined 160℃ heat-treatment wood was evenly distributed. With the increase of temperature, the volume of resin shrank to form regular spherical fine particles, which no longer blocked the pits. Compared to the untreated wood, the swelling and shrinkage efficiency of the impregnated wood all increased. Similar to the modification effect of the heat treatment on poplar wood, the hygroscopicity of this combined modified wood was significantly reduced than that of the impregnated wood, and the swelling and shrinkage efficiency all decreased, which indicated that heat-treatment can improve the dimensional stability of impregnated wood. Additionally, the effect of the test temperature (160, 180 and 200℃) of the heat-treatment on dimensional stability of this combined modified wood was not obvious.