Effect of gravity gradient in weak equivalence principle test

A high accuracy test of the weak equivalence principle (WEP) is of great scientific significance no matter whether its result is positive. We analyze the gravity gradient effect which is a main systematic error source in the test of WEP. The result shows that the uncompensated gravity gradient effect from the coupling term of the dominated gravity gradient multipole moment component q₂₁ and the relative multipole field component Q₂₁ contributes to an uncertainty of 1×10^-11 on the Eötvös parameter. We make a Q₂₁ compensation to reduce the effect by about 20 times, and the limit of the test precision due to this coupling is improved to a level of a part in 10¹³.