Abstract: Based on the introduction of fully non-normalized spherical harmonics,Clenshaw summation does not need a single spherical harmonics calculation.We compared Clenshaw summation method with standard forward column method in the calculation of time and analyzed the stability of these two methods by numerical tests.Then,we give the results of the tests.Finally,the applicability of geoid undulation computed based on Clenshaw summation method was discussed,which offers a reference for high-precision calculation of the geoid.