A dynamic reference deviation detecting method is used for detecting a deviation of a dynamic reference coordinate system. A coordinate detecting step is for detecting and recording a first initial coordinate and a second initial coordinate. A first coordinate variation calculating step is for calculating a difference between a first instantaneous coordinate and the first initial coordinate to obtain a first difference value. A second coordinate variation calculating step is for calculating a difference between a second instantaneous coordinate and the second initial coordinate to obtain a second difference value. A relative coordinate variation calculating step is for obtaining a relative difference value. A dynamic reference deviation determining step is for determining whether or not the dynamic reference coordinate system is deviated according to the first difference value, the second difference value and the relative difference value.