In this paper, a new measurement method is presented, This method is to use a three-coordinate measuring machine (CMM) to test the symmetry error of double keyway in a wheel hub bore. According to the minimum condition criterion of form and position error evaluation, and making use of the minimum tolerance zone of position error evaluation, two symmetry error formulas of double keyway in a wheel hub bore are deduced by geometric analysis. The problems may be encountered when using the formulas in the practical application are discussed. These formulas solve the measurement principle problem of double keyway in the engineering practice. In the end an example is put forward to verify this method and the formulas.