This paper establishes the accelerated life testing model, viz. the hybrid Weibull distribution model under multi-stresses (pressure, velocity and temperature) for typical mechanical product-aerial hydraulic pump. Direct toward the optimization difficulties with multi-parameters in Maximum Likelihood Estimation (MLE), this paper presents an Improved Float Genetic Algorithm (IFGA), which adopts the fuzzy algorithm in the float genetic algorithm to approach the global optimum solution. Application denotes that IFGA not only can obtain the global optimum solution but also can shorten the calculation time greatly.