The invention belongs to the field of vacuum-pumping equipment and provides a composite vacuum pump which comprises a pump shell, a gas inlet and a gas outlet, wherein the gas inlet and the gas outlet are formed on the pump shell; a plurality of levels of molecular drag pumps and Roots pumps, which are installed coaxially, are arranged in the pump shell; the molecular drag pumps are combined in parallel or series and are arranged at the part near the gas inlet; the Roots pumps are combined in series and are arranged at the part near the gas outlet; and the molecular drag pumps and the Roots pumps are combined in series. The composite vacuum pump provided by the invention has the advantages of high pumping speed, high ultimate vacuum, low energy consumption, small size and light weight andcan also acquire clean medium vacuum and high vacuum.