Aircraft engine rotors traditionally have low coaxiality after assembly. This is solved by the methods and devices described herein, having advantages that the rotors have high coaxiality after assembly, reduced vibration, easy installation, high flexibility, and improved engine performance. A measurement method and device use an air flotation rotary shaft system determining a rotary reference. An induction synchronizer determines angular positioning of a turntable. Using a four probe measurement device, a radial error of a rotor radial assembly surface and an inclination error of an axial mounting surface are extracted and an influence weight value of the rotor on the coaxiality of assembled rotors is obtained. All rotors required for assembly are measured and an influence weight value of each on the coaxiality of the assembled rotors is obtained. Vector optimization is performed on the weight value of each rotor and an assembly angle of each rotor is obtained.