Screw conveyor is an important tool of controlling earth pressure balance in EPB shield boring and plays a significant role in maintaining the earth pressure at the face of the shield. Usually EPB shield has a single screw conveyor. However, the single screw conveyor can not balance the earth pressure at the tunnel face in some high pressure areas. Therefore, EBP shield with double screw conveyors is designed to solve this problem. In the paper, mechanical model of the double screw conveyors in EPB shield is established on basis of EPB principle and mechanical formula for the pressure at the bottom of the double screw conveyors under static balance conditions is obtained, on basis of which the relationships between the pressure at the bottom of the double screw conveyors and the equipment parameters and the muck property parameters are discussed. The paper provides a simple method for the design, alteration, selection and evaluation of the double screw conveyors in EPB shield.