In this paper, we propose a new scenario generation algorithm called Combinatorial Testing Based on Complexity (CTBC) based on both combinatorial testing (CT) method and Test Matrix (TM) technique for intelligent driving systems. To guide the generation procedure in the algorithm and evaluate the validity of the generated scenarios, we further propose a concept of complexity of test scenario. CTBC considers both overall scenario complexity and cost of testing, and the reasonable balance between them can be found by using the Bayesian optimization algorithm on account of the black box property of CTBC. The effectiveness of this method is validated by applying it to the lane departure warning (LDW) system on a hardware-in-the-loop (HIL) test platform. The result shows that the bigger the complexity index is, the easier it is to reveal system defects. Furthermore, the proposed algorithm can significantly improve the integrated complexity of the generated test scenarios while ensuring the coverage, which can help to find potential faults of the system more and faster, and further enhance the test efficiency.