The utility model relates to a device for utilizing residual air of a Roots blower fan of a delivery system, comprising two delivery units, each delivery unit composed of two bulk heads in common use of one Roots blower fan and communicated with each other by a pipeline, wherein the end of the pipeline extends to form an exhaust pipe (a1,a2) and the exhaust pipes of two delivery units are communicated by a horizontal pipeline (b1). A break valve is respectively arranged on the end of the pipeline and two sides of the horizontal pipeline (b1) and a pressure meter is mounted on the front end of the break valve. Two vertical pipelines are mounted on the horizontal pipeline (b1) and each vertical pipeline is connected with one bulk head and one Roots blower fan and an electric butterfly valve (5) is mounted on an air inlet of the bulk head. The device mutually utilizes the residual air of the exhaust pipes in two common Roots blower fans and starts any Roots blower fan to use four bulk heads and when any Roots blower fan goes wrong, it is not necessary to stop the working of the delivery system.