Gas−liquid transportation is an efficient and economical transportation technology developed in recent years. It mainly uses some transportation equipment to simultaneously transport crude oil, associated natural gas, produced water, and so on for the purpose of reducing costs and energy consumption. In this paper, a double-chamber gas−liquid transferring device was selected as the research object. The VOF multiphase flow model of FLUENT software was used to simulate the gas−liquid two-phase flow performance under the design condition. The relationships between the two-phase flows, pressure, temperature, liquid level in the tank, outlet flow rate of the device, and time were calculated and analyzed. The results show that the operating cycle of the device can be divided into three processes, namely ‘suction-compression-discharge’, in which the cycle period formula is proposed as well. The pressures of gas and liquid in the device are basically the same, but the temperatures of the two phases are quite different in the compression process. In the compression process, the outlet valve is closed so that the outlet flow rate of the device is zero, and the gas compression process can be approximately treated as isothermal compression in engineering design. The comparison between the measured performance data in the oil field and the calculation results indicates that the calculation method in this paper is feasible for the performance prediction and optimization of the double-chamber gas−liquid transferring device.