Abstract: Rotors with curvic couplings,which are separately prestressed from the front part and the rear part,are often applied to modern turboprop and turboshaft engines.It is very important but difficult to determine the values of preloads for a rotor.The prerequisite of the axial relaxed/pressed forces caused by variety of rotor loads in operation is available,the criteria to determine the axial preloads of rotors are proposed in this paper,which takes into account synthetically the factors,such as tightness margin,strength margin,assembling relationship and etc.Hence the optimiztion model of the axial preloads is established,and the corresponding solution is presented.The computer program is developed according to the presented criteria and method.Finally,an example is given.