Abstract: For the problem that most of the algorithms will cross the diagonal obstacle to form an actual infeasible path in solving the shortest path in the multi-diagonal obstacle environment, an optimal ant colony algorithm combined with diagonal obstacle detection is proposed for the path planning of mobile robots. First of all, the condition obstacles are marked by diagonal obstacle detection. Then, the trigonometric selection method is adopted to select the passable and impassable condition obstacles accurately. Finally, the self-adjusting expected heuristic factor and pheromone updating strategy are put forward. The experimental result shows that this algorithm has the characteristics of high environmental adaptability, fast convergence speed and strong optimization ability, as well as it can effectively avoid the planned path crossing the diagonal obstacles.