The invention relates to a shunting type coal gas flow measurement device and a measurement method thereof. The shunting type coal gas flow measurement device mainly comprises a horizontal pipe, a liquid collection box, a coal gas collection box, a pressure transmitter, a coal gas flowmeter, a temperature transmitter and a computer. When coal gas flows through the horizontal pipe, natural separation phenomenon occurs because of the action of gravity, liquid and solid impurities in the coal gas are deposited towards the bottom of the pipe, dry coal gas are gathered on the upper part of the horizontal pipe, a part of the coal gas is further purified and enters a shunting measurement circuit, corresponding measurement signals are obtained and the coal gas returns to the horizontal pipe, the corresponding measurement signals are immediately transmitted to a coal gas flow export module in the computer, and total flow of the dry coal gas is finally obtained. In addition, the liquid and solid impurities in the coal gas are collected into the liquid collection box through a porous wall of the lower part and discharged to a recovery system through a liquid discharge valve. The invention can greatly reduce the volume of the measurement device, simplify a separation method, improve real-time property of measurement, automation degree and measurement accuracy and facilitate the widespreadapplication of the measurement device and method in engineering.