Knee pain caused by blowing air conditioner may be caused by cold, knee synovitis, and old knee injury. 1. Cold: When blowing the air conditioner, the continuous stimulation of cold wind or low temperature can cause spasm of the soft tissues around the knee joint, resulting in pain in the knee joint area due to cold. 2. Knee synovitis: trauma or long-term strain can cause knee synovitis, which often leads to increased fluid accumulation in the joints, accompanied by pain in the joints, especially when subjected to cold, damp and other stimuli, which will aggravate the pain in the knee joints. 3. Knee joint old injury: mostly seen in the knee joint old fracture or dislocation, due to the body injury site has not been fully recovered or more sensitive, in the cool air or humidity and other environmental stimuli, may cause pain in the old injury site. Blowing air conditioning knee pain should try to pay attention to keep warm, to avoid the knee part of the cold, usually can wear knee pads, if the pain fails to alleviate the recommendation to the hospital.