For the importance of the stable scanning phase in the single-fin TSA' system efficiency, the computer simulation which is based on using quaternion to represent the Euler kinematics was used to list and analyze the strong asymmetric aerodynamic force structure's impacts to this phase. The vertical falling velocity, scanning frequency, scanning angle and scanning distance can be influenced by the variation of the single-fin's length, angle, the weight of the ammunition, the heavy object's weight on the single-fin and the ammunition's moment of inertia to its central symmetry axis. The computer simulation results show that the ideal scanning parameters can be got by adjusting the structure parameters. The rules extracted from the computer simulation also provide significant theoretical foundation in the real single-fin TSA's design.