The utility model provides a mass flowmeter used at the well head of a coalbed gas well, relating to a coalbed gas well dynamic monitor technology. The utility model is characterized in that a baffle is installed in a liquid inlet tube; the liquid inlet tube is connected with a buffer tube installed in a casing; a magnet is installed on the lateral side of a tipper; and a counter is installed in the casing. The beneficial effect of the utility model is that the mass flowmeter can prevent the disconnected current of the liquid from striking with relative great force, so that the liquid entered the measuring tipper is relatively slow which is favorable to correct measurement. The length of the buffer tube is about equal to the length of the tipper. A lot of small holes are arranged on the buffer tube, making the liquid flow into the tipper evenly which is also favorable to correct measurement. The magnet is installed on the tipper and the counter is installed in the casing, so automatic measurement can be realized. The device has simple structure, low price and small measurement error.