An in situ exploitation-separation-backfilling integration apparatus for natural gas hydrates is disclosed, consisting of a cyclonic inhalation device for coarse fraction, a jet flow device for sand discharge and a spiral cyclone device for fine fraction. The cyclonic inhalation device for coarse fraction is provided with a vortex trough and a cyclonic auxiliary flow channel; the jet flow device for sand discharge mainly consists of a sand discharge sliding sleeve, a sand discharge jet cylinder and a spring, wherein the sand discharge sliding sleeve can control the spraying out of hydraulic fluid and it is provided with a sand discharge butting head; inside the spiral cyclone device for fine fraction is a tapered structure and its upper portion is provided with a centering bracket.