This study investigated the heat-transfer behavior of heat-treated and phenolic resin-impregnated bamboo bundle slabs during the hot-pressing process. The significance of these findings lies in their potential to drive advancements in hot-pressing technology, contribute to energy-conservation efforts, and facilitate emission reduction within the bamboo scrimber industry. In this study, the variations in temperature and vapor pressure were investigated during the hot-pressing of bamboo slabs under various conditions, including hot-pressing temperatures (140 °C, 150 °C, 160 °C, and 170 °C), hot-pressing holding times (15 min, 20 min, 25 min, and 30 min), and hot-pressing pressures (4 MPa, 5 MPa, 6 MPa, and 7 MPa). This was achieved using thermocouple sensors and a self-made vapor pressure-monitoring system. The results indicated that higher hot-pressing temperatures significantly increased the heating rate, peak temperature, and core-layer vapor peak pressure of the bamboo bundle slab, with the vapor peak pressure at 170 °C being twice that at 140 °C. Furthermore, extending the holding time had a lesser effect on increasing the peak temperature of the slab but significantly increased the peak vapor pressure in the core layer. Thus, increasing the hot-pressing pressure proved beneficial for slab heating but had a lesser effect on the surface and core-layer peak temperatures. The core-layer vapor pressure of the slab subjected to a hot-press pressure of 7 MPa was 1.8 times higher than that at 4 MPa.