Abstract: In order to study the backwater calculation of an overflow bridge of pipe culvert，a straight river model of trapezoidal river section was constructed，and an overflow bridge of pipe culvert model was constructed according to the design index of actual engineering parameters.On this basis，a formula method and HEC-RAS software were used to calculate，analyze and discuss the single-line bridge backwater results and the double-line bridge superimposed backwater.The results showed that: ① Both methods can be used to calculate the backwater of the pipe culvert overflow bridge，and the calculation accuracy of the two methods was equivalent.② When using the formula method to calculate，it is necessary to reasonably select the weir flow formula according to the bridge and river section forms，and the main parameter weir flow coefficient C0 in HEC-RAS software can be obtained by the formula method.③ In practical engineering，the combination of the two methods can make the calculation results of backwater more reasonable.