Objective: To investigate the level of physical activity and its influence in elderly patients after knee arthroplasty. Methods: A total of 90 elderly patients undergoing knee arthroplasty who were admitted to our hospital from January 2020 to January 2021 were selected. The International Physical Activity Questionnaire, the Physical Activity-Self-Regulation Questionnaire, and the Exercise Self-Efficacy Scale were used to evaluate the level of physical activity level, physical activity motivation, exercise self-efficacy 3 months after surgery, and the factors affecting physical activity level were analyzed by single factor and multiple factors. Results: Among the 90 patients, 22 cases were low physical activity levels, 55 cases were moderate physical activity levels, and 13 cases were high physical activity levels. Among them, daily physical activities consume the most energy, followed by exercise and leisure entertainment, and again for daily life. transportation. There was a statistically significant difference in the physical activity level of patients with different genders and marital status (P<0.05). Multivariate analysis showed that marital status, body mass index (BMI), knee function and pain were associated with moderate physical activity levels Influencing factors (P<0.05); gender, marital status, physical activity-self-regulation, exercise self-efficacy, BMI, knee function and pain were the influencing factors of high physical activity level (P<0.05). Conclusion: The physical activity level of elderly patients after knee arthroplasty is moderately low. Clinically, attention should be paid to the patient's gender, marital status, physical activity-self-regulation and exercise self-efficacy, and postoperative physical activity intervention should be strengthened.