During the desing of channel transect,the paper brings forward golden section method,which is 0. 618methods. In order to reduce the calculation volume of the natural depth of water ho and bottom-width b which apply trial calculation method and gralphic method ,and improve the calculate precision ,the mathematical model has been built up,the writer combines example to explain the train of thought ,the result shows that the calculation precision is high, the correctness is tested and verified by the result which is calculated by hand. It can be referred tO the hydroelectric works.