The key issue in gas metering of alternative fuel vehicle is to obtain low emission and accurate air-fuel ratio. A hot wire mass air flow sensor can directly monitor the air flow by using thermal transfer amount in an unit time to keep the hot wire at a certain temperature. Surveys were conducted regarding this method and it was verified that this method enables to monitor mass gas flow in applications such as Compressed Natural Gas(CNG) and propane(C3H8). The gas passage body for this sensor, which consists of a 10mm diameter bypass and a main pass has been surveyed and developed. This electrical sensing device for CNG has been completed and its performance was verified with a CNG flow test stand and a CNG engine. We have found that this thermal transfer monitoring method is not affected by a pressure change.