The invention provides an oilfield associated gas recovery method and device. The device comprises a triangular rotor compressor. An air inlet, a liquid inlet and a discharge outlet are formed in a cylinder body of the triangular rotor compressor. A triangular rotor arranged in the cylinder body can achieve forward rotating and reverse locking. The air inlet is communicated with a low-pressure airoutlet of an oil well casing. A high-pressure oil outlet of an oil well oil pipe is communicated with a main pipe. A first branch and a second branch on the main pipe are correspondingly communicatedwith the liquid inlet and the discharging opening. The connection direction of the portion, between the first branch and the second branch, of the main pipe refers to the connection from the high-pressure oil outlet to an outer conveying pipeline. By using the pressure difference formed by high pressure at the liquid inlet and the low pressure at the discharging outlet, the triangular rotor operates so that the low-pressure associated gas in the oil well casing can be pumped and recovered without additionally providing power for pumping and recovering the low-pressure associated gas, the compression recovery of the low-pressure associated gas in the oil well casing can be completed, and the recovery cost of the associated gas in the oil well casing is greatly reduced.