Linearity and non-linearity simulation are used in hydrological calculation.Least square method is of-ten applied to simulate curve generally,but this method ignores that the relative errors should be less than certain percent between fact sur vey point and simulated curve.In order to improve it's precision,weight least square method(WLSM)for non-linearity and least distance square method(LDSM)for linearity relative equation are provided to improve traditional least square method.Comparing to traditional method,LDSM's result is more practicality;relative to traditional one orientation method,its linear equation is not changed by the selection of coordinate system.A case study is applied to discuss it primarily.