Path planning is an optimization problem that is crucial for robot or UCAV. Among the optimization approaches, we focus in this paper on a new hybrid modified Rapidly Exploring Random Tree algorithm (RRTs) and Differential Evolution (DE), for solving the optimization path planning problem to generate a fast and optimal 3D collision-free path under complex environment. We demonstrate the proposed algorithm performance through comparative analysis with Improved Bat algorithm (IBA). The results demonstrated the robustness and effectiveness of the proposed algorithm for generating an optimal free collision path in a short time, which is suitable for the UCAV applications.