The invention provides a method for calculating gross vehicle weight. The method includes the steps that a gravity acceleration sensor, a controller and a vehicle original engine ECU which are installed on the vehicle are utilized, the controller figures out the current gross vehicle weight based on a
vehicle driving kinetic equation by obtaining engine information, vehicle information and dip angle information and acceleration information and then outputs the current gross vehicle weight information outwards, wherein the dip angle information and the acceleration information are output by the gravity acceleration sensor. The vehicle information comprises the current gearbox gear speed ratio information, the final ratio information, the tier rolling
radius information, the rolling damping coefficient information, the
drag coefficient information, the conversion coefficient information of automobile rotary weight,
transmission system mechanical efficiency information,
clutch switching state information and the like. The invention further provides a fuel-saving control method. The method includes the steps that the current gross vehicle weight is obtained through calculation, the ratio of the current gross vehicle weight to vehicle full-load gross weight is converted into a loading state, and the ECU selects corresponding
engine power output gears according to the received loading state information. The method for calculating the gross vehicle weight and the fuel-saving control method have the advantages that the number of used sensors is small, and calculation results are accurate.