To improve the measuring accuracy of laser trackers,the geometric errors of a tracker were analyzed, and the error calibration and error correction methods for a tilted mirror in the tracker were explored. An error model for the titled mirror was established based on vector analysis and coordinate transformation, and the error correction formulation for geometric space coordinate of the tracker was deduced. Then, a high precision error calibration device was built based on a multi-mirror polygon, an adjustable reflected mirror and autocollimators. The calibration device was used to analyze the error calibration method, and the system simulations were used to research the influence of mirror tilt error on angle and coordinate measurement errors. The error calibration test shows that the mirror tilt error is 4″. The tested error was induced to the coordinate correction formulation, and the spatial length measurement errors of the system before and after correction were tested. The results indicate that the measuring error of the laser tracker decreases by about 2×10-6, which shows that the error calculation and error correction methods are effective. The method improves the measuring accuracy without changing the hardware structure of the system.