Measurement point distribution in contact measuring large aspheric optical surface was researched. By the radial and uniform measurement points with different density distributions, various surface deviations represented by different Zernike polynomials were sampled respectively. Then, the maximum PV and RMS errors were calculated and analyzed. Measurement results of a 1.8 m parabolic mirror were taken as examples, and it indicates that the low density radial measurement point distribution can meet the measurement needs at the forming and coarse grinding stages because the surface deviations show large rotate-symmetrical forms. Moreover, the uniform distribution of measurement points is an effective way to improve measurement accuracy at fine grinding and initial polishing stages, for the main surface deviations are astigmatism or other asymmetrical aberrations. This method can guide the measurement point distribution, control the measurement error caused by distribution to be less than 1/5 of surface error, and can improve measurement accuracy efficiently.