Abstract: Internal performance of unsteady flow of counterf low thrust vectoring no zzle has researched base on numer ical simulat ion. The results show, in the former of half aun??steady period, the perfo rmance parameters are almo st the same under at tachment and deat tachment cases, but have a great dif ference in the after of half a period. It is the representation of the flow hy steresis. T he hyster esis leads the at tachment of main f low diff icult to depart from the w all. The origin of hysteresis may be relate to shear lay er. The evolv ement of counterf low and cof low shear layer present a difference behave, and may play a common role in main flow deat tachment. Lastly, the results of unsteady flow point out, counterf low thrust vectoring nozzle is a ef ficiency f luidic vecto ring nozzle.