A method for warning deflation of tires which can detect the deflation of 2 wheels at the same axle including a following axle, the simultaneous deflation of 4 wheels or the abrasion of tires only by the information of wheel speeds is provided. The method comprises the steps of: detecting the rotational information of each of tires; calculating and storing wheel speeds, vehicle accelerations, slip ratios of front and rear wheels, traveling distances and radius of traveling circle from the rotational information of said respective tires; calculating moving average of the vehicle accelerations and the slip ratios of front and rear wheels; accumulating the traveling distances and storing the moving averages of the vehicle accelerations and the slip ratios of front and rear wheels; determining regression coefficient and correlation coefficient of the slip ratio of front and rear wheels on the vehicle acceleration; determining the slip ratio of front and rear wheels when the vehicle acceleration is zero; determining whether the pressures of at least 2 wheels at the same axle or 4 wheels are simultaneously reduced or not, based on the regression coefficients and the slip ratio of front and rear wheels while the vehicle acceleration is zero; and warning deflation of tires.