The present invention relates to a KBBF family nonlinear optical crystal-prism coupler and its method of fabrication. The coupler comprises: a KBBF family crystal with two smooth surfaces; transition layers each of which is deposited on respective one of the two smooth surfaces of the KBBF family crystal; and a pair of prisms each of which optically contacts with respective one of the activated transition layers. The present invention further provides a KBBF family nonlinear optical crystal-prism coupler that comprises: a KBBF family crystal with two smooth surfaces; a pair of prisms each of which has a smooth surfaces; first transition layers each of which is deposited on respective one of the two smooth surfaces of the KBBF family crystal; and second transition layers each of which is deposited on a smooth surface of respective one of the pair of prisms, wherein the first and second transition layers are integral by optical contact. The coupling between the KBBF family crystal and the prisms is achieved by optical contact through transition layers to improve bonding strength.