The present disclosure discloses an integrated device for millisecond-level gas phase catalytic cracking reaction and separation, comprising: a horizontal inertial cyclone separator, a horizontal inertial cyclone separator feed tube, a pyrolysis vapour inlet, a regenerated catalyst inlet, a horizontal inertial cyclone separator central tube, a cracked vapour outlet, a catalyst outlet tube, a spent catalyst silo, a first loop-seal, a riser regenerator, a settling tank, a gas-solid separator, and a second loop-seal.