HEC-RAS one-dimensional mathematic model can be applied to the calculation of constant flow and unsteady flow. It is often used in the fields of rainfall runoff analysis，river hydrodynamic，flood process analysis and so on. Taking the post disaster reconstruction of the Minjiang river channel（Leshan section） as an example，we use HEC-RAS model calibrate to analyze and calculate the water surface line of this section according to the measured terrain，measured diversion ratio and measured water boundary line of the river channel，and study the applicability of HEC-RAS model in the calculation of the design minimum navigable water level of the braided river section. The results show that the HEC-RAS model has good calibration results in the study area，has good applicability，and can provide economic and effective technical support for channel regulation of braided rivers.