The invention discloses a device for a control surface unfolding wind tunnel test of a free flight model, which comprises a flexible head, a flexible body, a folding rudder and an unfolding mechanism, wherein the unfolding mechanism comprises a push rod which is equipped with a round boss on the rear section, a front nut, a rear nut, a big spring and a small spring, a front end blind hole, a rear end blind hole and a middle through hole communicated with the two blind holes are disposed inside the flexible body, an installation groove used to install the folding rudder and a spindle installation hole are disposed in an flexible body wall of the rear end blind hole, the push rod passes through the middle through hole, the big spring is sleeved into the push rod from the front end and installed in the front end blind hole and then limited by the front nut and the bottom wall of the front blind hole, the small spring is sleeved into the push rod from the rear end and fixed on the round boss, a rudder plate of the folding rudder is installed in the installation groove by a spindle, the rear nut is connected on the push rod by threads on the rear side of the folding rudder, a chamfer is disposed on the front end of the rear nut, the top end of the chamber is contacted with a coordination face on the rear end of the folding rudder when the folding rubber is folded, and the flexible head is installed on the front end of the flexible body after installation of the unfolding mechanism. The device is simple in processing and convenient in installation.