Recently, the needs of modification or new installation of reactors in desulfurization and hydrocracking pocesses are increased because of the great demand of naphtha, kerosine and gas oil instead of fuel oil, and the necessity of deep reduction of sulfur content in diesel oil and long duration of operation. In this connection, the state of the up-to-date design technology of high pressure desulfurization reactors in desulfurization and hydrocracking processes is introduced.