The invention discloses an electromagnetic coil bobbin used in reactor as well as an inner bobbin and an outer shell thereon, wherein more than one cut-off grooves are provided on the inner bobbin and the outer shell and uniformly distributed on corresponding inner bobbin or outer shell such that the inner bobbin and the outer shell of which the material of the main body is metal have excellent high-temperature resistance and avoid generation of induced eddy current, and such that the electromagnetic coil can generate a more uniform magnetic field while operating, thus achieving technical effects of reducing or avoiding eccentric wear, reducing or avoiding partial excessive wear, etc., and realizing the objectives of improving and raising movement performance of CRDM.