Path planning is important in the research of a mobile robot (MR). Methods for it have been used in different applications. An automated guided vehicle(AGV), which is a kind of MR, is used in a flexible manufacturing system(FMS). Path planning for it is essential to improve the efficiency of FMS. A new method was proposed with known obstacle space FMS in this paper. FMS is described by the Augmented Pos Matrix of a Machine (APMM) and Relative Pos Matrix of Machines (RPMM), which is smaller. The optimum path can be obtained according to the probability of the path and the maximal probability path. The suggested algorithm of path planning was good performance through simulation result: simplicity, saving time and reliability. Path planning is important in the research of a mobile robot (MR). Methods for it have been used in different applications. An automated guided vehicle (AGV), which is a kind of MR, is used in a flexible manufacturing system (FMS) . A new method was proposed to improve the efficiency of FMS. A new method was proposed with known obstacle space FMS in this paper. FMS is described by the Augmented Pos Matrix of a Machine (APMM) and Relative Pos Matrix of Machines (RPMM ), which is smaller. The optimum path can be taken according to the probability of the path and the maximal probability path. The suggested algorithm of path planning was good performance through simulation result: simplicity, saving time and reliability.