The life cycle of aviation equipment comprises more than one mission stage， yet most of the current ALT optimal design studies only focus on the situation of one mission stage. A two-stage ALT optimal design method under integrated environmental stresses is proposed. The Latin hypercube design theory is used to determine the overall stress level combination of the two-stage test， and to solve for the combination of stress levels between the pre- and post- stage. Taking the minimum sum of the asymptotic variance of the estimated P quantile life of the product under normal stress levels in the two-stage test as the optimization criterion， a mathematical model of the optimal design is constructed to solve the problem of sample allocation between the pre- and post- stage. The case analysis shows that the prediction accuracy of the method is superior to that of the traditional method， and the parameter sensitivity analysis shows that the optimal test plan determined by the method has robustness. This method provides a new idea for the ALT design of multi-stage task products in practical engineering.