Abstract: Objective To evaluate the cardiac function and exercise tolerance affected by acute high altitude exposure using submaximal treadmill exercise test and provide a safe, scientific and standardized method for working capacity evaluation under acute high altitude exposure. Methods In August 2014, 40 male soldiers undergoing military training at high altitude(4 000 m) were recruited as high altitude group and another 40 volunteers lived at low altitude(60 m) as plain group, the blood pressure and heart rate of two groups were recorded, and they all had treadmill exercise test. Results There was no significant difference in age, weight, blood pressure and heart rate between the two groups. Pre-exercise systolic blood pressure in the high altitude group was significantly higher than that in the plain group (127.5±14.1) mmHg vs(118.5±13.9) mmHg(1 mmHg=0.133 kPa), P=0.005); after treadmill exercise, there was no significant difference in systolic blood pressure between the two groups. There was no significant difference in pre-treadmill diastolic blood pressure between the two groups, but the average post-treadmill diastolic blood pressure of the high altitude group was significantly higher than that of the plain group (73.7±11.7) mmHg vs(63.3±10.5) mmHg, P=0.000). The average heart rate of the high altitude group before treadmill exercise was significantly higher than that of the plain group (98.4±12.8)/min vs(67.4±8.8)/min, P=0.000); the heart rate of the high altitude group after treadmill exercise was significantly higher than that of the plain group (115.9±17.6)/min vs(100.7±26.6)/min, P=0.004). The oxygen saturation in the high altitude group was significantly lower than that in the plain group (88.9±2.6)% vs(98.9±1.1)%, P=0.000), and oxygen saturation in the high altitude group after treadmill exercise was significantly lower than that in the plain group (77.1±5.8)% vs(97.8±1.0)%, P=0.000). The exercise duration of the high altitude group was significantly lower than that of the plain group (457.8±80.1) second vs(485.1±8.1) second, P=0.038), and the metabolic equivalent value(METs) in the high altitude group was significantly lower than that in the plain group (8.94±1.34) METs vs(10.04±0.07) METs, P=0.000). Eight volunteers suffered adverse events in the high altitude group, and no adverse events occurred in the plain group. No plate positive and malignant endpoint events was found in the plain group and the high altitude group. Conclusion Performing submaximal treadmill exercise test at high altitude(4 000 m) is relatively safe and feasible, and it can be used for assessing the work capacity after acute high altitude exposure.