UAV path planning is a multi-constraint optimization problem, including terrain threat, radar threat and its flight ability. This work proposes an integrated constraints method to plan the flight path of unmanned aerial vehicle(UAV) based on two-step mechanism. In the first-step of the path planning, the differential evolution optimization is adopted based on the multi-population strategy; The Lévy motion optimization of the marine predator algorithm is adopted in the second-step of the path planning. The integrated constraint mechanism is adopted to update the cnstraint strategies dynamically in the searching process, preventing the decrease of the feasible solutions and the stagnation of the searching. Compared with the typical existing constraint mechanisms, the proposed method has a good convergence and stability, and can effectively solve the UAV path planning with the complex multi-constraint.