Abstract: Taking into account the interaction of an electron with bulk longitudinal-optical (LO) and surface longitudinal-optical (SO) phonons, we study the ground state energy and self-trapping energy of the bound Magnetpolaron in a polar slab by using the Huybrecht’s linear combination operator method. the ground state energy and the self-trapping energy are all derived as function of slab thickness. includes two parts, one is , the other is ; taking KCl as an example , and all reduce with the increase of the slab thickness, and when the slab thickness d is more than 5nm, is about to a stable number. especially, increases when there is the magnetic fild, because of the interactions was strengthened between the electrons and phonons.