Abstract: The aerodynamically compensating pitot tube, which is used to reduce the error of the pressure altimeter of an airplane,is studied by the mixed difference computation of transonic small disturbance. The static pressure distribution of the compensating pitot tube and the positive pressure field in front of the nose inlet are calculated. The static pressure error produced by the nose inlet is compensated by the negative pressure at the static pressure orifice of the pitot tube. The. computed results and prediction agree very well with the wi nd tunnel and flight test data.