In order to measure the radius of curvature and conic factor of an off-axis aspheric mirror, a new method to measure the conic surface with a laser tracker is proposed. The data processing procedure after spatial 3D cordinates are obtained with the laser tracker is clearly explained. An off-axis reflecting aspheric mirror is tested in the experiment and the radius of curvature and conic factor are obtained using nonlinear least square fitting method. The root mean square error (RMSE) is only 1.6 μm while the coefficient of determination is up to 0.999999954. Besides, the results of our method and the existing methods are nearly the same. Both theoretical analyses and experimental results demonstrate that this is a simple, general and easily operated method, which benefits from the fast and reliable data processing. The proposed method meets the measurement requirements of conic aspheric mirrors.