Objective To evaluate and compare the changes in physiological indicators before and after heat acclimatization training in personnel with different endurance capacities. Methods A total of 170 healthy adult male volunteers were recruited and assigned to high or qualified endurance groups based on their 3-km running endurance test performance, and were further randomly assigned to 4 groups: high endurance training (HET) group (n=60), qualified endurance training (QET) group (n=50), high endurance control (HEC) group (n=30), or qualified endurance control (QEC) group (n=30). The HET and QET groups underwent 7 and 12 d of outdoor heat acclimatization training, respectively. All subjects underwent a baseline test 1 d prior to training and a heat acclimatization efficacy evaluation test on the 2nd day after completion of training. During the tests, core temperature, heart rate, body weight, water intake, blood oxygen saturation, and blood pressure were monitored, and sweat samples were collected to detect electrolyte concentrations. Results Compared with the baseline test, both the HET and QET groups showed decreases in core temperature and reductions in sweat Na⁺ and Cl^- concentrations during the efficacy evaluation test; the QET group exhibited decreases in mean heart rate and maximum heart rate, whereas the HET group had opposite trends; and the HET group showed increases in body weight loss and water intake, while the QET group showed no significant change in body weight and a decrease in water intake. During the efficacy evaluation test, compared with their respective control groups, both the HET and QET groups showed decreases in core temperature and sweat Na⁺ and Cl^- concentrations; the QET group also showed reductions in mean heart rate, maximum heart rate, and body weight loss, whereas the HET group showed no significant changes. The heat acclimatization training had no significant effects on blood oxygen saturation, blood pressure, or the concentrations of K⁺, Ca²⁺, and Mg²⁺ in sweat. Conclusion Personnels with high endurance can achieve heat acclimatization following 7 d of training and those with qualified endurance following 12 d. Regardless of whether endurance capacity is rated as high or qualified, the core temperature and the concentrations of Na⁺ and Cl^- in sweat decrease after heat acclimatization.