A method capable of automatically switching operation modes is applied to a multi-functional mouse device which has a first operation mode and a second operation mode. The multi-functional mouse device can move over a plane formed by a first axis and a second axis perpendicular to each other, and includes a coordinate positioning unit suitable for the second operation mode. The method includes detecting whether the coordinate positioning unit generates a first axial signal, detecting whether the coordinate positioning unit generates a second axial signal within a first predetermined period, determining whether continued time of the first axial signal and the second axial signal exceed over a second predetermined period, and determining whether the multi-functional mouse device is switched from the first operation mode to the second operation mode according to a determination result.