Tears in posterior horn of medial meniscus mainly included horizontal tear, transversal tear, radial tear, complex tear, and bucket handle tear. We analyzed and compared the risk factors for radial tear and horizontal tear in the posterior horn of medial meniscus. A total of 407 consecutive cases who received arthroscopic treatment of medial meniscus tears were analyzed retrospectively. Among them, 103 cases were radial tear in posterior horn of medial meniscus and 107 were horizontal tear. Clinical data records included patients' age, gender, duration of symptoms, body mass index, trauma history, and slope angle of tibia, valgus angle of knee, and grading of cartilage (Outerbridge Grades) were collected and analyzed. In addition, multiple-factor nonconditional logistic regression was adopted to analyze the related risk factors in these two types of medial meniscus tears. The two groups have no difference in age, trauma history, slope angle of tibia, and duration of symptoms but have significant difference in gender, body mass index, and valgus angle of knee and grading of cartilage. Multiple factors analysis indicated that valgus angle, age, and grading of cartilage were risk factors in medial meniscus tears. Patients with posterior horn tear in medial meniscus have higher incidence among senile osteoarthritis, while radial tear was more likely to occur in elderly patients with knee-joint varus and serious cartilage degeneration.