Abstract: Deep metal mine stopes are typically characterized by a harsh thermal environment with high temperature, high humidity, and low air velocity, which imposes considerable heat load and heat stress on workers and threatens occupational health and operational safety. To identify the thermal environmental characteristics and hazard-causing mechanisms of mining and excavation workplaces at different depths and under different operation types, and to provide quantitative support for ventilation and cooling optimization, a field investigation was conducted in a deep gold mine under the actual ventilation conditions during the second-stage infrastructure construction. Eleven measuring points were arranged in typical underground workplaces to monitor air temperature, relative humidity, and air velocity. Based on human heat balance theory, the convective, radiative, and evaporative heat dissipation components as well as the body heat storage rate （S） were calculated. In combination with the heat stress index （HSI） and the PMV−PPD model, a multi-index evaluation framework integrating heat balance, heat stress, and thermal comfort was established to comprehensively assess the thermal environment of multi-level and multi-type underground workplaces in the deep metal mine. The results showed that the air temperature at the measuring points ranged from 29.3 °C to 34.7 °C, the relative humidity was generally higher than 90 %, and the air velocity in most workplaces was only 0.2−0.5 m/s. The body heat storage rate S was positive at all measuring points and approached 100 W/m² in some deep workplaces. The HSI were far greater than 100 %, while PMV was close to 3 and PPD was close to 100 %, indicating a severe thermal hazard and extremely poor thermal comfort. The analysis further revealed that the high-temperature, high-humidity, and low-air-velocity environment in deep mine workplaces significantly weakened human convective, radiative, and evaporative heat dissipation, among which restricted evaporative cooling was the key factor leading to increased body heat storage. According to the thermal environmental differences at different mining levels, a graded control strategy of increased air supply, dehumidification, and local cooling was proposed, which can provide an engineering reference for thermal hazard prevention and ventilation-cooling system optimization in deep metal mines.