FCD-based traffic navigation system is getting more and more attention from countries all over the world. Shortest path algorithm is one of the key techniques of a traffic navigation system. Since classical Dijkstra algorithm and heuristic A* algorithm cannot support some constrained conditions in practice, and existing algorithms supporting constraints require the road network to be modified ahead and have low efficiency. The paper studies the model of road network, and analyzes two types of constraints, one-way street and intersection turning prohibitions, then proposes the constrained A* algorithm and gives the Heuristic function. Finally, the paper tests and analyzes the algorithm, and evaluation performance of the prototype system which employs it. The result shows that the algorithm’s efficiency is fairly good.