To solve the autonomous navigation problem in complex environments, an efficient motion planning approach called EffMoP is presented in this paper. Considering the challenges from large-scale, partially unknown complex environments, a three-layer motion planning framework is elaborately designed, including global path planning, local path optimization, and timeoptimal velocity planning. Compared with existing approaches, the novelty of this work is twofold: 1) a heuristic-guided pruning strategy of motion primitives is newly designed and fully integrated into the search-based global path planner to improve the computational efficiency of graph search, and 2) a novel soft-constrained local path optimization approach is proposed, wherein the sparse-banded system structure of the underlying optimization problem is fully exploited to efficiently solve the problem. We validate the safety, smoothness, flexibility, and efficiency of EffMoP in various complex simulation scenarios and challenging real-world tasks. It is shown that the computational efficiency is improved by 66.21% in the global planning stage and the motion efficiency of the robot is improved by 22.87% compared with the recent quintic Bézier curve-based state space sampling approach.Note to Practitioners-This paper is motivated by the challenges of motion planning for mobile robots. We propose an efficient motion planning approach by combining a search-based global path planner and an optimization-based local trajectory planner, which is able to guarantee efficiency, safety, smoothness, and flexibility. In addition, we employ a decoupling framework for local trajectory planning to take into account the real time performance, motion efficiency, and safety. Extensive simulation and experimental results in complex environments show the effectiveness of the proposed motion planning framework. In the future research, we will concentrate on motion planning of mobile robots in large-scale and unstructured field environments.