Judging method of vehicle loading condition

To provide a judging method of loading condition of a vehicle and a tire deflation warning system capable of preventing alarming four-wheel diffusion for a vehicle with heavy load. The judging method of vehicle loading condition including the steps of detecting rotational speeds of wheels mounted on a vehicle, calculating a judging value of tire pressures based on the difference of the sum of rotational speeds of two pairs of wheels located at the opposing corners of the vehicle and detecting an acceleration to a lateral direction of the vehicle, wherein the loading state of the vehicle is judged by the change of a primary coefficient when relation between the acceleration to a lateral direction and the judging value of the tire pressures is primarily approximated. The tire deflation warning system including means for detecting the rotational speeds of wheels mounted on a vehicle, calculating the judging value of the tire pressures based on the difference of the sum of rotational speeds