The some five-axis machining center was investigated, and it divided ten subsystems. Based on analysis of fault data, the distribution of fault time submits to Weibull distribution, the distribution function and reliability function of each subsystem were confirmed. The reliability allocation model with the constraints of cost is established based on reliability prediction to get optimal reliability allocation results of the complicated mechano-electronic system. The most growth potential of the reliability of subsystem and growth situation of reliability of each subsystem could be got by using this method. The reliability allocation is an important part of reliability design, because its result influences system design directly. This provides reference for design improving of this series of new products.