The large oil depot map is different from city and mountainous region whose maps are complex. The map of large oil depot is very regular, oil tanks and other buildings arranged neatly and the roads of the oil tank area are straight. On the basis, the classic A^* algorithm is improved in this paper. On the one hand, according to the characteristics that the map of oil depot is simple and the number of search nodes is relatively small, the data structure of the Open table in the A^* algorithm is improved, to accelerate the search speed and the ranking algorithm is used to improve the search efficiency. On the other hand, because roads in the oil depot are straight, so we divide roads into two parts: roads with obstacles and barrier free roads, to improve the search efficiency. Experimental results show that, with the combination of the two improved methods, the time of searching roads is declined definitely by 6.86%.