A refrigeration cycle device and a two-stage rotary compressor thereof. The two-stage rotary compressor includes a housing with a gas injection chamber and two cylinders disposed therein; the gas injection chamber connected to a liquid reservoir disposed outside of the housing and a gas injection pipe; a first cylinder in communication with the gas injection chamber; a second cylinder connected to the liquid reservoir, and having a sliding vane groove and a compression chamber with a piston disposed therein in communication with the gas injection chamber; a sliding vane, received in the sliding vane groove when the gas injection chamber is in communication with the liquid reservoir, with an outer end and the sliding vane groove defining a backpressure chamber in communication with the gas injection chamber; and with an inner end abutting against the piston when the gas injection chamber is in communication with the gas injection pipe.