The invention provides a device for locking and dismounting a tail support rod of a wind tunnel test model. The device includes a device body, a first tip cone assembly, a second tip cone assembly and a spanner; the device body includes an ejection screw, a pull claw, a beam, a bolt and a nut, wherein the pull claw and the beam are connected through the bolt and the nut, the ejection screw is connected with a first dismounting tip cone and a second dismounting tip cone, and the beam is connected with a first positioning tip cone and a second positioning tip cone; the first tip cone assembly includes the first dismounting tip cone and the first positioning tip cone; the second tip cone assembly includes the second positioning tip cone, the second dismounting tip cone, two expansion sleeves, a guiding bolt and a guiding nut; and a guiding groove is designed between the expansion sleeves. A method for locking and dismounting the tail support rod of the wind tunnel test model includes tail support rod locking, wedge-shaped key dismounting and tail support rod dismounting methods. The device and method can reliably mount and conveniently and rapidly dismount the wedge-shaped key and the model tail support rod, thereby avoiding influence of repeated knocking on the wedge-shaped key on balance measurement accuracy and a model mechanism.