The earth conveying and pressure maintaining of screw conveyors play an important role in the safe and efficient boring of EPB shields. The working principles and influencing factors of the earth conveying and pressure maintaining of screw conveyors are systematically analyzed. Conclusions drawn are as follows: 1) The earth pressure balance in the boring of EPB shields includes the pressure balance between inside chamber and outside chamber, the pressure balance inside the screw conveyor, and the earth input/output volume balance, which can be realized by controlling the volume of earth conveyed. 2) When the earth enters the screw conveyors, the water/soil pressure in the chamber is resisted by the gravity of the earth and the friction with the screw rod, lamina and the inner side of the conveyor, so as to keep stable earth conveying. 3) The earth behavior, which has great influence on the earth conveying and pressure maintaining of screw conveyors, can be improved by injecting ground conditioning agents into areas ahead of the cutter heads and into the chamber. 4) Regarding the structure of the screw conveyor, the pressure maintaining effect can be improved by means of reducing the pitch, adopting discontinuous screw and double screw conveyors. 