The invention discloses a self-propelled self-tensioned fixing mechanism, is a fixing mechanism of a tunnel outline forming device, and solves the problem that a thin-wall drill is deformed so that the device can be damaged while the outline excavation is performed in the tunnel. The self-propelled self-tensioned fixing mechanism comprises a diaphragm energy accumulator, a tension oil cylinder, an external connecting pipe component, a connecting plate, an upper connector, a central rod, a slider, a connecting key, a cone, a spring, and a lower connector. The rest components are the expansion conical head components except the diaphragm energy accumulator, the tension oil cylinder, the external connecting pipe component and the connecting plate; the central rod is in screwed connection with the piston rod of the tension oil cylinder; the upper end of the upper connector is in screwed connection with the external connecting pipe component; the lower end of the upper connector is in screwed connection with the cone; the slider is connected with the central rod through the connecting key; the slider is slid on the cone; the cone is in screwed connection with the lower connector; and the spring is located between the lower plane of the central rod and the upper plane of the lower connector. The self-propelled self-tensioned fixing mechanism uses the single oil cylinder to push the fixing mechanism into a fixing hole, and uses the oil cylinder to push continuously, so the fixing mechanism is tensioned to the external wall, the recoil force supported by the device is bigger, and the tensioning force generated by the tensioning mechanism is bigger. The structure is simple, the cost is low, and the application prospect is extensive.