Objective To explore the effect of low-load resistance training on physical fitness in aged adults. Methods Select the aged adults who will go to the outpatient Department of Rehabilitation Medicine of Peking Union Medical College Hospital between June 1, 2020 and May 31, 2021. The aged adults were randomly divided into three groups by using the method of random number table: medium intensity aerobic training group (aerobic training group), standard-load resistance training group (standard-load group) and low-load resistance training group (low-load group). The basic information, exercise endurance (peak power, peak oxygen uptake), exercise cardiopulmonary function [peak heart rate, predicted peak heart rate, peak minute ventilation (VE), ventilatory equivalent for carbon dioxide at anaerobic threshold (EqCO2 during AT)], muscle strength, and muscle oxygen related indexes were collected blindly before the first exercise and after 12 weeks of training, respectively. To compare the differences of the indexes before and after training. Results A total of 90 patients were enrolled, 30 in each group. There was no significant difference in age, sex, height, weight and body mass index among the three groups (P>0.05). There was no significant difference in cardiopulmonary endurance, cardiopulmonary function, muscle strength, muscle oxygen related indexes between the groups before and after training (P>0.05). Except for the indexes related to cardiac function (peak heart rate, predicted peak heart rate) and resting muscle oxygen level (P>0.05), other indexes related to pulmonary function, cardiopulmonary endurance, muscle strength, and time of muscle oxygen falling to the valley in the three groups were statistically significant compared with those before training (P<0.05). Except for peak power, peak oxygen uptake and time of muscle oxygen falling to the valley (P>0.05), the difference of muscle strength before and after training in the three groups was statistically significant (P<0.05), including grip strength, chest push, sitting rowing, leg extension, hip abduction, body bending and horizontal push and push, and the low-load group was better than the aerobic training group (P<0.05), but the improvement of body bending and horizontal push and push in the standard-load group was better than the low-load group (P<0.05). Conclusions Low-load resistance training, standard-load resistance training and aerobic training have almost the same effect on improving the physical fitness of the elderly. Low-load resistance training is superior to medium intensity aerobic training in improving muscle strength, which is an effective method to improve the physical fitness of the aged adults.