Abstract: There are empty regions near the poles which are two spherical caps with angle radius of 96.7°, as the inclination of GOCE satellite is 96.7°. This paper will discuss the influence by combining the methods of invariants. Firstly it derives the formulas which show the influence of the polar gaps on the gravity field recovery, and then analyzes the magnitude and prosperity of the influence by simulation. The results show that different degrees will influence each other due to the destruction of orthogonality, especially on low orders. The method of remove-restore can effectively solve the problem of accuracy lose due to the polar gaps, but different reference models will give different results. However, even so, GOCE can still provide geoid with accuracy of several centimeters not in polar region.

Key words: GOCE, gradient invariants, harmonic analysis, polar gaps