The invention relates to a measurement device of flow rate of dusty gas and a measurement method thereof. The measurement device comprises more than one positive pressure taking pipe and a negative pressure taking pipe. The positive pressure taking pipes stretch into a to-be-measured pipeline and are parallel to air flows in the to-be-measured pipeline. Positive pressure taking openings and a negative pressure taking opening are respectively arranged in the positive pressure taking pipes and the negative pressure taking pipe. A positive pressure flow guiding mechanism is arranged at each of the positive pressure taking openings. A negative pressure flow guiding mechanism is arranged at the negative pressure taking opening. The positive pressure taking pipes and the negative pressure taking pipe stretch out of the to-be-measured pipeline and then are connected with a differential pressure gauge via a lead-out pipe which is perpendicular to the positive pressure taking pipes and the negative pressure taking pipe. The positive pressure taking pipes are communicated with the positive pressure end of the differential pressure gauge. The negative pressure taking pipe is communicated with the negative pressure end of the differential pressure gauge. The lead-out pipe and the to-be-measured pipeline are sealed by a sealing cover. The outer side face of the sealing cover is fixed at the opening of the to-be-measured pipeline via multiple fixing buckles. The beneficial effects are that the measurement device is simple in structure, convenient to operate and capable of preventing blocking phenomena caused by dusty gas during the measurement; effects on measurement results are reduced; and measurement precision is improved.