An electromagnetic measuring probe device for measuring a thickness of a dielectric layer of a circuit board and a method thereof are disclosed. The circuit board has at least one dielectric layer, at least two conductive layers and a test area. The test area has a test pattern and a through hole. The electromagnetic measuring probe device has a probe-measuring unit, an external conductive element, plural magnetic powder groups, and a maintaining unit. The probe-measuring unit has a transparent tube and an internal conductive pin. The external conductive element electrically connects with the test pattern. The conductive layers and the internal conductive pin generate a magnetic field while the probe-measuring unit enters into the through hole. The magnetic powder groups magnetically attracted are gathered to positions corresponding to thickness-range positions of the conductive layers and held by the maintaining unit, thus a gap between the two dielectric layers is obtained.