This study aimed to evaluate the effect of intraarticular injection with platelet-rich plasma on knee osteoarthritis. A total of 250 patients with stages I–III osteoarthritis from December 2018 to June 2020 were included in this study. All the patients had received autologous PRP injection (3 ml) into the affected knee joint every week for totally 3 injections. The VAS score and WOMAC index were used to evaluate knee function before and at 3 days, 1 month, and 3 months after injection. A total of 250 patients were enrolled in this study, including 130 patients in the PRP group and 120 patients in the control group. The content of platelets in PRP of patients in the PRP group was 958.0 ± 283.1 × 109/L. The VAS score and WOMAC index of patients in the PRP group before treatment were not significantly different from those in the control group. At 3 days, 1 month, and 3 months after PRP treatment, the VAS score and WOMAC index of the PRP group were significantly lower than those of the control group. PRP is effective in treatment of knee osteoarthritis. The pain symptoms can be alleviated at 3 days after injection.