Objective: The purpose of this study was to observe the distribution of muscular vein dilatation in patients before artificial joint replacement and to identify the risk population, and to provide theoretical basis for clinical prevention of thrombosis. Methods: A retrospective analysis was performed on patients who underwent primary knee and hip replacement in the joint center of our hospital from March 2015 to July 2017. Thrombus was screened and muscular vein was assessed by 2 sonographers 1-3 days before surgery. All patients were divided into dilation group and non-dilation group, and the risk population was determined by statistical analysis of the differences in age, body mass index, gender, hypertension, smoking history, varicose vein history, malignant tumor history, surgical type, lateral gender, osteoarthritis, femoral head necrosis and other factors between the two groups. Results: a total of 569 patients were included in the study, including 155 males and 414 females, with a mean age of 63.33 years (range 19-87 years) and a mean body mass index of 25.21±4.02kg/m2 (range 15.21-40.79kg/m2). The preoperative mean diameter was 0.56±0.24cm (range 0.10-1.83cm). Among them, 238 cases (41.8%) were found in the intermuscular vein dilatation group. The age of the dilatation group was significantly higher than that of the non-dilatation group (P < 0.001), and body mass index (P < 0.001), knee surgery (P < 0.001), osteoarthritis of the knee (P < 0.001), and femoral head necrosis (P=0.007) were also found to be risk factors for dilatation. Age stratification showed that the value of intermuscular vein dilatation increased with age (P < 0.001). In the regression analysis, age and large body mass index were risk factors for preoperative intermuscular vein dilatation in joint replacement population. Conclusion: intermuscular vein dilatation is a common phenomenon in artificial joint replacement. Advanced age and large body mass index are the predisposing factors of intermuscular vein dilation in patients with artificial joint replacement.