The invention discloses a V-cone based low-gas-content gas-liquid two-phase flow liquid-phase flow rate online measurement device and method. The device includes a data acquisition and processing system, a measuring pipeline, a V-cone throttling device, a first differential pressure transmitter, a second differential pressure transmitter, a pressure transmitter and a temperature transmitter; the V-cone throttling device is located in the measuring pipe, the first differential pressure transmitter is used for detecting gas-liquid two-phase flow differential pressure between an upstream pressureobtaining point of the V-cone throttling device and a coned-tail pressure obtaining point of the V-cone throttling device, the second differential pressure transmitter is used for detecting gas-liquid two-phase flow pressure loss between the upstream pressure obtaining point of the V-cone throttling device and the downstream pressure obtaining point of the V-cone throttling device, the pressure transmitter is used for detecting the gas-liquid two-phase flow pressure in the measuring pipeline, and the temperature transmitter is used for detecting the gas-liquid two-phase flow temperature in the measuring pipeline; the measuring pipeline is communicated with a to-be-measured pipeline. The device and the method can achieve the online measurement of the low-gas-content gas-liquid two-phase flow liquid-phase flow rate, the cost is low, and the structure is simple.