Abstract: An automatic calculation method of the fixture location error is presented. The automatic calculation mechanism of the method, the coordinate system hierarchy of workpiece-fixture assembly system and its establishment rules are introduced and discussed firstly. Then, the fixture locating elements are grouped into the compound location element based on the machine assembly model, and the compound rules of the compound location element which contact with same location datum of the workpiece are described. At the last, a prototype software to calculate the location error automatically is illustrated and an example is given to verify the prototype software.