Abstract: Missile radome is complicated revolving body. In order to establish the datum of inner-surface before precision internal grinding, it is necessary to reconstruct the free curved inner-surface from a large amount of discrete measured data. A bicubic B-spline method based on least squares techniques to reconstruct 3D surface of radome's inner-surface is presented, and successfully applied in the precision grinding system of missile radome. The results after internal grinding prove that the inner-surface reconstructed by this method is smooth and accurate.