In order to test middle and low precision asphere and measurement of asphere during grinding and polishing, a new method by extending the ability of laser tracker is proposed. The testing principle is analyzed, and the testing procedure is devised. The coordinate of several points on the tested asphere can be measured by the laser tracker, and the figure error can be calculated by analyzing the testing data and CAD model of the asphere. An off-axial aspheric surface with the aperture of 420 mm×270 mm is measured by this method, the surface map by this method is consistent to the entire surface map from the null test, and the relative error of the PV and RMS error between null test and this method is 6.22% and 3.37%, respectively. The proposed method provides another quantitive measurement for testing large aperture aspheres without any assistant optics, and the data processing and testing operation are very convenient.