Abstract: In this paper, a new method of curred surface fitting (NMOCSF) for physical variable in a limited area is proposed. According to the principle of filtering, the physical variable is fitted multiply. In case of each fitting, the places of the maximum and the minimum of the fitting function are in accordante with that of the original function. The contrastive experiment shows that the accuracy of the NMOCSF is higher than that of the finite element method. The synoptic systems with the scale about 220km can be identified by the NMOCSF. The fitting function are continuous and smooth in the calculated area and the NMOCSF is stable. Thus, the practical value of the NMOCSF is higher than that of the finite element method in the diagnostic analysis.