Fixtures are used to locate and constrain firmly a workpiece during machining operation. Flexible and efficient fixturing has become an important issue in flexible manufacturing systems and computer integrated manufacturing system. Locating planning is the basis of the fixturing design, which has a direct influence on the quality of the clamping scheme and the machining quality of workpiece. This paper presents a new approach for locating planning of workpiece. Firstly, it will automatically select the primary locating surfaces with consideration of 5 influence factors: constraint freedoms, surface feature, valid locating area, tolerance relationship and surface roughness. Then the other locating surfaces are determined by retrieving similar workpieces under the guideline of 4 locating methods which will make the best of already available locating planning. Finally the optimal locator layout is fast achieved with GA with the goal of minimal locating tolerance.