Abstract: The operation of gas oil hydrotreating unit and deep catalytic cracking (DCC) unit of SINOPEC Anqing Branch is introduced and the influence of hydrotreated feedstock on the operation of DCC unit is analyzed. Results show that the hydrotreated mixed gas oil can be used as a high quality feedstock for DCC unit. The product distributions of DCC unit is improved remarkably: light oil yield increases by 2.89 percentage point, and the yields of dry gas, coke and low value products decrease significantly. Meanwhile, the quality of products is improved greatly as well, items including sulfur content, induction period, olefins content and aromatics content of DCC gasoline can meet the specifications of gasoline for national emission standard III.