Sore knees on rainy days may be caused by degenerative lesions of the knee joint, autoimmune diseases and so on. 1. Degenerative lesions of the knee joint: When degenerative lesions of the knee joint occur due to aging or repeated wear and tear, the symptoms of rainy day knee pain may occur. 2. Autoimmune diseases: autoimmune diseases may also lead to knee pain on rainy days, the pathogenesis is mainly due to autoantigen and antibody perversion in the knee joints, rainy days also affects the blood flow around the joints, the above symptoms, common diseases such as rheumatoid knee osteoarthritis, gouty knee osteoarthritis and so on. There may be other reasons for knee pain on rainy days, it is recommended to go to the hospital in time, improve the examination to clarify the cause of the disease, and then give targeted treatment or treatment under the guidance of the doctor.