The traditional method has the problem of large indication error in the range of 247mm-256mm from the measuring point. Therefore, a calibration method of measuring error of outer diameter micrometer based on Monte Carlo method is proposed. The UGS model of the outside micrometer is made and imported into the CAE software for processing, and the finite element analysis model of the outside micrometer is constructed. The vibration error model of measuring force change is constructed by Monte Carlo method, and the measurement error of external micrometer is analyzed by this model. Through the two gauge calibration compensation method, the measurement error of the external micrometer is compensated, so as to realize the error calibration. The experimental results show that the indication error of this method is smaller than other methods in the range of 247mm-256mm from the measuring point, which can effectively improve the error calibration effect.