Laser tracker has been introduced successfully for geometric deviations calibration of multi-axis machine tools. In this paper, a new method called “pose measurement principle” is developed for measuring geometrical error of rotary axes by means of a single laser tracker and NC precise table. The reflector is mounted on the NC precise table with eccentricity, and the NC precise table is mounted on rotary table. A single laser tracker located at different base stations in order is used for coordinate determination of three fixed points of the reflector to get the pose information of rotary axes, then calculate the pose deviations and identify all the errors. For the error identification, first of all, with the extension of the definition of geometric errors, the 6 geometric errors is represented by pose deviation. Second, 3 angular errors are identified geometrically first, then eliminate the angular errors of all measuring coordinates to obtain the 3 straightness errors. Finally, the 6 errors mathematical model for rotary table is developed. The validity of the proposed method has been confirmed by simulations and experiments. From both of them, it has been confirmed that the proposed method gives precise results and is able to apply to the measurement of rotary axes effectively.