To verify the effect of softening treatment on the cutting force during slicing of veneers, an experiment was performed using a veneer slicer with steam injection heating function. Several conditions were set to soften the experimental materials of poplar (Populus L.), eucalyptus (Eucalyptus robusta Smith), pine (Pinus massoniana Lamb.), and Chinese fir (Cunninghamia lanceolata (Lamb.) Hook.). The cutting force was detected by the YE7600 signal analysis system. The results showed that the cutting force increased with increased slicing thickness. The cutting force was observed to follow the order, from high to low for the conditions of being soaked in cold water, then steam heated, water-poached, and steam heated again. Compared to the case of non-steam heating, the effect of steam heating on reducing the cutting force was satisfactory, and the maximum decrease percentage reached 83.1%. The cutting force was positively related to the wood density and hardness, and the cutting stroke had a great influence on the cutting force. After being softened, the four kinds of fast-growing wood were sliced into veneers with ≤ 6 mm thickness, and the cutting force was generally no more than 6850 N.