A high speed steel composite roll billet which has not only favorable interface quality of outer shell and core material and regular outer shape, but also shallow oscillation marks and compact microstructure was manufactured by electromagnetism continuous casting for cladding method. When the relations of the technique parameters are proper. The results indicate that the microstructure of the roll billet is composed of chilled solidified layer, dendrite zone, interfacial zone of bimetal and core material zone. The microstructures of the outer shell material include martensite, bainite, residual austenite and some small labyrinth-shape, small-short lath-shape, or dollop-shape eutectic carbides. The microstructure of the core material is slice-shape pearlite and a little ferrite along boundary of cells. The interface region microstructure of bimetallic composite roll consists of diffusion region, chilled solidified layer and columnar grain region