Abstract: The finite volume method（FVM） of the second-order Godunov scheme was used to simulate the long-distance water conveyance system with pressurized and open channel sections. Firstly, the governing equations of pressurized pipe flow and open channel flow were respectively discretized according to FVM, the flux was calculated by the Riemann solver, and the MINMOD slope limiters were introduced to avoid spurious oscillations during data reconstruction. The virtual-boundary approach was presented to achieve a unified computation scheme for all the control volumes at the internal domain and boundaries. In an open channel calculation time interval, several pressure calculations were carried out to realize the joint calculation of pressurized pipe flow and open channel flow. The model proposed in this paper was compared with the traditional method of characteristics（MOC） to verify the accuracy of the proposed model, and the sensitivity of the calculation time interval was analyzed. The results show that when the Courant number is less than 1.00, MOC will produce large calculation errors in both pressurized pipe flow and open channel flow, while FVM calculations are more accurate. The results of the combined hydraulic calculation of pressurized pipe flow and open channel flow were compared with that of the independent calculation of the pressurized section. The latter result is more conservative, which makes the economics of the construction design stage poor. Therefore, the joint calculation of pressurized pipe flow and open channel flow proposed in this study is of high necessity.