The invention relates to a mud discharging structure for a medium and small type earth pressure balance shield machine. The mud discharging structure comprises a screw machine, a transfer mud discharging box, a mud discharging pipe and a vacuum generating device; the screw machine is arranged in a shield body of the shield machine, the transfer mud discharging box is arranged in a slag dischargingport of the screw machine, the transfer mud discharging box is connected to the vacuum generating device through a mud discharging pipe, the transfer mud discharging box includes a stirring device and at least one soil modification agent addition port, and the transfer mud discharging box is used for stirring and improving soil discharged by the screw machine to the transfer mud discharging box to the flow-formed state, and the vacuum generating device extracts the improved flow-formed slag soil through the mud discharging pipe. According to the mud discharging structure, the transfer mud discharging box with a stirring and slag soil improving system is arranged, slag soil can be subjected to secondary stirring, and the requirement for cutter head and soil tank slag soil improvement is reduced.