The invention discloses a servo system position IP controller model-free self-correcting method based on fractional order. The method includes: setting a reference model, exciting a system to obtain an offline database, initiating the related parameters of the system, updating the database according to input and output data newly collected at a current moment, selecting similar data queues according to a similarity criterion function, selecting the order of a fractional order controller, and using particle swarm optimization algorithm to perform self-correcting on fractional-order IP controller parameters. The method has the advantages that the fractional order feature of the system is considered, performance such as overshoot, rising time, error convergence speed and controller parameter variation is appraised comprehensively, the instantaneity of the system is guaranteed by using the similarity criterion function, the method is unaffected by unmodeled dynamics, and the robustness, disturbance rejection ability and control precision of the system are increased.