The invention provides a method for measuring an axial gap between a centrifugal impeller and an impeller casing, comprising the following steps of: a. assembling the rotor to an air intake casing anda rear support casing to center the rotor and form an axial gap between the centrifugal impeller and the impeller casing; b. measuring the distance between the rotor and the rear support machine to obtain H1; c. releasing the assembly relationship between the rotor and the air intake casing, axially moving the rotor to eliminate the axial gap between the centrifugal impeller and the impeller casing; d. measuring the distance between the rotor and the rear support casing to obtain H2; e. subtracting H2 from H1 to obtain the axial gap value between the centrifugal impeller and the impeller casing. The method for measuring axial gap between centrifugal impeller and impeller casing can accurately measure the axial gap value between the centrifugal impeller and the impeller casing when the rotor is completely centered. This solves the problem of large measurement error caused by the rotor's uncenteredness, and solves the problem that cannot be measured due to the influence of the rear support mechanism.