Cangzhou Refinery has implemented the technicaltransofrmation of diesel ultra-deep hydrodesulfurization (RTS) against thediesel hydrotreating unit during the device overhauling. A set of RTS reactoris added to the diesel hydrotreating unit to connect with the original reactorsin series and the new catalyst produced by SINOPEC Catalyst Co., Ltd. isapplied to achieve the goal of deep desulfurization of products. After thetransformation, the sulfur content of the product is lower than 10ppm, thusmaking the factory have the capability of producing China IV disel oil ahead ofschedule.