The small aspect ratio flying wing layout has become an advanced fighter development platform due to its high stealth and high aerodynamic efficiency. The particularity of the layout reduces the lateral stability, which makes it face the problem of wing rock instability and affects the maneuvering of the aircraft performance and flight quality. Through wind tunnel test and numerical simulation method, the rock characteristics and mechanism of small aspect ratio flying wing scalar wing were comprehensively analyzed, and a nonlinear aerodynamic model coupled with the effect of roll angular rate was developed. The results show that the small aspect ratio flying wing layout has the wing rock problem after the pitch angle of 28°, and the curve of the roll moment coefficient with the roll angle in the limit cycle oscillation process is not a stable hysteresis loop. During the oscillation process of the limit cycle, the roll damping derivative changes with the roll angle rate as a quadratic function, which makes the roll moment coefficient hysteresis loop in a clockwise state. The influence of the roll angle rate is introduced into the conventional dynamic derivative model, and the simulation can be accurately predicted limit cycle oscillation.