To study the flow loss characteristics of a shaft tubular pump, the FBM-CC turbulence model was used to conduct unsteady calculations on the internal flow field of the shaft tubular pump based on the URANS method. The entropy production theory was used to quantitatively analyze the flow loss characteristics of the shaft tubular pump under different flow conditions. The result shows that the FBM-CC turbulence model can effectively predict the hydraulic performance of the shaft tubular pump, which is in good agreement with the experimental results. The flow loss of the shaft tubular pump is in the order of the impeller, outlet channel, guide vane and inlet channel. The main source of impeller energy loss is turbulent dissipation, accounting for up to 92%. Vortex and flow separation can lead to local high entropy production areas. Large number of vortices exist at the impeller hub in critical stall conditions and the flow at the rim is relatively stable. The deep stall conditions are affected by the tip leakage flow, and flow separation occurs at the impeller inlet rim. As the flow rate is further reduced, the streamline of the inlet channel is affected and separation vortices appear at the leading edge of the blade.