Techniques from the probablistic perturbation method and con-straint random direction method are employed to present the practical and ef-fective method for the reliablity optimization design of vehicle half-axle on thecondition of known probabilistic characteristics of original random variables.The theory formulae of reliability optimization design for hollow half-axle areobtained. The respective program can be used to obtain the reliability optimi-zation design parameters of hollow half-axle accurately and quckly.