In order to give a better prediction of the pressure maintaining performance of shield screw conveyor with earth pressure balance, the pressure difference between inlet and outlet of screw conveyor was analyzed on the assumption that the conditioned soil is a viscoplastic fluid, and the pressure maintaining mechanism was explained from the perspective of energy conversion. A steady calculation of the flow state of conditioned soil in screw conveyor was carried out by using computational fluid dynamics (CFD) method, where Herschel-Bulkley model was used to describe the rheological behavior of conditioned soil, and the rotation of screw blade was fully considered by using multi-reference frame (MRF) method. The influence of soil fluid parameters and the working parameters of screw conveyor on pressure maintaining performance was obtained, and a comparison between the simulation results and the indoor test results was carried out. The analysis result shows that the pressure maintaining performance of screw conveyor increases with the increase of yield stress, viscosity index and power-law index, where the influence of viscosity index and power-law index is more obvious. The mechanical energy loss of screw conveyor is basically proportional to the rotating speed of screw and soil removal efficiency. Fast rotating speed and high soil removal efficiency result in excellent pressure maintaining performance. The relationship between the mechanical energy loss, rotating speed and soil removal efficiency can be estimated by using binary linear regression model. The trend of simulation results is consistent with the indoor test results, and the Herschel Bulkley rheological model can be used to calculate the pressure maintaining performance of screw conveyor. However, the prediction of pressure maintaining performance is conservative. Finally, based on the results of numerical calculation, the optimization process of screw conveyor pressure maintaining performance is proposed.