Abstract: The detailed research on theoretical foundation of SCHA is given;and the model of applying SCHA to fit GPS level height is put forward,which is to achieve the transformation between GPS geodetic height and level height.A new model to adjust the SCHA model——ASHA model is discussed.It solves the problem in SCHA model,which is there is not a good method to compute the real rank of Legendre function quickly now.The test results show that both the inside and outside precisions can be controlled in centimeter rank.