Abstract: Aiming at the problem of rail joint collapse defect in the on-site welding process of YHGQ-1200 pneumatic rail car, taking the welding re-use rail of Boxiao line rail change construction welding as an example, according to the problems in the process of type inspection and the actual problems in the field, the causes of rail joint collapse defect are analyzed, and the solutions of rail joint collapse defect are summarized. The field measurement shows that the scheme can effectively solve the problem of collapse angle of rail welded joint, which has certain reference significance for rail welding.