Abstract: Wind-tunnel free-flight tests with biplanar optical system were conducted at Mach 6 in the hypersonic wind tunnel, to investigate the dynamic stability of the spinning blunt cone. Due to the application of a two-plane orthogonal optical system in wind-tunnel free-flight tests, both views in horizontal and vertical plane can be recorded synchronizingly. And the two views of coning motion can also be observed directly. With the record angular motion results in both views, identification method of biplanar is studied. Then the static and dynamic derivative coefficients of the models are acquired, and dynamic stability criterion is obtained.