Abstract: Aiming at the problems during the local quasigeoid/geoid determination by traditional resi-dual point mass model, such as large system error, big amount of basic data requirement, low computational efficiency and singularity of inverse process, a new approach is presented in this paper called semi-free position point mass based on the gravity field approximation principle. Compared with the traditional model, the plan coordinates of the new one are stationary, while the depths are free. The method is established by a kind of iterative algorithm using the relationship between the nearest points. Then, the algorithm is optimized using the weights calculated by surrounding points based on their distances from the calculating point, then to obtain the best fitting result, a kind of new adaptive method to determine the optimal weighted point number is presented. Results show that the theories presented in this paper achieve higher accuracy than traditional ways, with the advantage of little system error, less modeling data, no singularity and higher accuracy. In summary, using the method to fit local quasigeoid/geoid is feasible, and the adaptive one is better.