Abstract: This paper adopts the Quine-McCluskey method of finding prime implicants in a logical expression to isolate all the largest rectangle free area in a specified environment,the free rectangle areas are represented as nodes in a connected graph. We present the double-direction A algorithm to search the optimal nodes path,which is suitable for this kind of graph search. Then the idea of as many as possible nodes look ahead is put forward to plan the actual geometric path. Our method is proved to be very effective by two simulations.