The stage-discharge relation curve fitting was made by using the orthogonal functions, based on the observed data from the Wanyugou station. The error statistics and “three terms” test were made for the curves at the various levels, from which the suitable curves were selected to meet the error indexes in the standard of hydrologic data processing and the required accuracy of determination of relation curve, and then analysis it was made by comparing with the results from manual determination of relation curve. The results show the fitted curve of the orthogonal functions can meet the requirement from hydrological data processing.