The invention discloses an automatic proportioning device for composite alcohol diesel oil. The automatic proportioning device consists of a cleaning tank, a diesel oil tank, a plurality of alcohol storage tanks, an alcohol collecting tank, a measurement and control platform, a stirrer, a cosolvent tank, a heat dissipating device, a composite alcohol diesel oil storage tank and a composite alcohol diesel oil collecting tank, wherein the cleaning tank is respectively connected with the diesel oil tank, the alcohol storage tanks and the stirrer; a diesel oil injecting pipeline and a diesel oil output pipeline are connected onto the diesel oil tank; an eighth electromagnetic valve and a first flowmeter are arranged on the diesel oil output pipeline; alcohol injecting pipelines and alcohol output pipelines are respectively connected to the alcohol storage tanks; an electromagnetic valve and a flowmeter are arranged on the corresponding alcohol output pipeline; the stirrer is connected with the cosolvent tank through a pipeline. The automatic proportioning device has the benefits that human errors in the proportioning process are effectively avoided while the labor intensity of workers is reduced, and the production efficiency of finished products is greatly improved.