Abstract: In the paper,the intrinsic structure of the gravity field is first introduced into the study of the normal ellipsoid's interior.After the further relationship among the intrinsic geometric properties is built,the relation between the geometric properties and physics of the interior is presented,which follows,the basic differential equation on the condition of quasi-equlibrium is set up,and finally the method to determine the intrinsic geometric poperties and density of the ellipsoid is given.It's shown that Wavre formula and Clairant equation which are on the condition of equilibrium and ellipsoidal approximation can also be derived in this way.