The invention belongs to a sand discharging and pressure relieving single-flow device used in a petroleum drilling industry and specifically relates to a sand discharging and pressure relieving single-flow device used in a process of extracting petroleum through a submersible screw pump. The sand discharging and pressure relieving single-flow device is characterized in that a shell body is mounted on a lower connection hoop; a piston is mounted in the shell body; a piston spring is mounted under the piston; a sealing ring is mounted outside the piston; a plurality of oil leakage holes are machined in the middle position of the shell body; an upper shell body is mounted at a position at the upper part of the shell body through a connection hoop; an upper connection hoop is mounted on the upper shell body; a guide sleeve is mounted at the position in the upper connection hoop; a guide rod is mounted in the guide sleeve; a valve element spring is mounted outside the guide rod; and a valve element is mounted at the position under the guide rod. The sand discharging and pressure relieving single-flow device can work stably and reliably, has remarkable economic benefits and can be applied to a variety of work, such as recovery of oil fields, oil leakage in coal-bed gas water drainage, well washing, sand discharging and contamination removal.