The utility model relates to a viscous crude thermal recovery completion technology field, in particular to instrument is right to tertiary reducing of heating power formula for gas injection. End screw thread connection center bushing pipe under the top connection of this instrument, outer hydraulic cylinder cover suit are in the central bushing pipe outside, and the piston is installed to the annular space troops under one's command end that forms between outer hydraulic cylinder cover and the central bushing pipe, and the airtight annular space of piston upper end places the thermal expansion's chemical agent, and the piston lower extreme is equipped with the thrust ring, and the thrust ring can be down along central bushing pipe under the promotion of piston, and the thrust ring can not go upward, and the thrust ring lower extreme is equipped with tertiary slider and sets upright or straight the wing. The utility model discloses an using the gas injection heat as the power supply, can realizing tertiary reducing, will be progressively enlarge and set upright or straight, it is big that expanding rate is set upright or straight to the reducing, and well application scope is wideer, can support the pipe of well completion in the pit cluster at the horizontal segment, avoid with wall of a well contact down, reduce pipe cluster gravity to packer setting's influence, sit for the extrusion of packer and provide safeguard, set upright or straight the intensity height.