Abstract: A single-Stage, double-catalyst hydrocracking technology (FDC technology) is developed by FRIPP, which converts heavy gas oil to maximum clean diesel. FDC technology has been successfully applied in six commercial units. The commercial results in Jinling branch hydrocracking unit with 1.5 Mt/a as well as Hainan petrochemical co., LTD hydrocracking unit with 1.2 Mt/a show that the middle distillate yield is high (78.99%, 74.87%, respectively) and chemical hydrogen consumption is low（2.31%, 2.15%, respectively）. The FDC technology possesses the properties of simple flow sheet and high LHSV of the single-stage hydrocracking technology and remedy for some shortcomings of single-stage hydrocracking technology such as bad feed adaptability, short running cycle of catalyst and bad quality of hydrocracking product. Moreover, the FDC technology is also featured by good quality of products and flexibility for product slate and low production cost as well.