Abstract: The fitting of water level and discharge relationship curve is an important link in the compilation of hydrological data, and its accuracy directly affects the quality of data compilation results. With the development of hydrologic modernization, the number of hydrologic stations increases rapidly, and the traditional manual alignment method is difficult to meet the work needs. In order to improve the quality of hydrological data compilation, a comprehensive comparative analysis is conducted on the accuracy and results of least square method, programming solution and orthogonal function fitting curve. The results show that the orthogonal function model is superior to the programming solution and the least square method. The method can quickly realize the fitting of the relation curve of water level and discharge, which is not only convenient for computer analysis and processing, but also eliminates human subjectivity without human intervention. The orthogonal function fitting curve can meet the requirements of hydrological data integration, improve work efficiency and alignment accuracy, and has the value of popularization and application.