Healthy fitness is considered to be closely related to good health. Nowadays, in a modern society, people are less and less active, and high-nutrient intake is increasing. In the face of high-intensity work and life pressure, people’s leisure and entertainment time will increase relatively. When people are deeply aware of the importance of good physical fitness and regular exercise for health. Physical fitness training can bring some positive factors to the body. The purpose of this paper is to study the rationality of fitness assessment indicators for cardiorespiratory fitness in medical systems. In this paper, the cardiopulmonary function and gas metabolism test (K4b2 exercise cardiopulmonary function tester) was carried out by step-by-step incremental load test (CS3000). The subjects wore a breathing mask and a heart rate monitor on a power bicycle for 5 min to measure the gas metabolism in a quiet state. The incremental load motion is then completed on the power bike. At the same time, the three-axis physical activity monitor produced by ActiGraph in the United States was used to test the energy metabolism during exercise and training. The exercise load starts from 25 W, the rotational speed is 60 r/min, each stage increases by 25 W, the load of each stage lasts for 2 min, there is no interval between the levels, and the heart rate, blood pressure and RPE value at the end of each stage are recorded. The experimental results demonstrates that the method has a significant effect on the functional fitness of the elderly with cancer (P < 0.01). The exercise frequency and exercise time have the most significant influence on the fitness of the elderly with cancer (P < 0.001). The muscle strength, flexibility, balance quality and cardiorespiratory strength of the upper and lower limbs were significantly positively correlated with the exercise frequency and each exercise time, but not by the exercise intensity (P > 0.05).