The digital measurement of free-form surface is the key to machining quality inspection for surface parts, and the basic requirement of digital measurement is how to realize the adaptive distribution of sampling points with the curvature feature. The traditional sampling methods were limited to the surface known mathematical model. This paper was concerned with free-form surface sampling with CAD model. Firstly, an algorithm of extracting data points from free-form surface was proposed, which transformed the free-from surface into intersection lines. Secondly, the B-spline interpolation was utilized to acquire the parameter expression of each line. Then the curvature measure function was defined on the basis of the curvature and the spline mass was determined taking the curvature measure as density. A new sampling method was presented based on dividing the spline mass equally. On this basis, the sampling process for surface was formulated, which realized the adaptive distribution for surface based on CAD model. The computer simulations show that the suggested method can approximate the curves and surfaces with higher precision comparing against other sampling methods.