Objective To analyze the characteristics of the muscle strength around the knee joint of chondromalacia patellae patients, and to explore the difference with normal people.Methods In March, 2021, 70 knee-onset chondromalacia patellae patients (experimental group) and 35 normal people (control group) were measured isokinetic muscle strength of flexion and extension of knee in angular velocities of 60°/s and 180°/s.Results At 60°/s and 180°/s, the peak torque, the peak torque-to-weight ratio and the total work of the flexor and extensor muscles on the affected side in the experimental group were lower than that of the control group (U > 1097.0, P<0.001). The peak torque, the peak torque-to-weight ratio and the total work of the flexor and extensor muscles at 60°/s and extensor muscles at 180°/s were lower on the affected side than on the healthy side in the experimental group (|Z| > 2.121, P<0.05). The peak torque ratios at 60°/s and 180°/s were more in the affected knees than in the healthy knees of experimental group and in the control group (U > 1810.0, |Z| >3.691, P<0.01).Conclusion The explosive force and endurance of the knee flexor and extensor has weakened in patients with chondromalacia patellae, and there is imbalance in knee joint muscle strength.