In order to reveal the relationship between the structural parameters of the top foil of the multi-leaf bump foil gas dynamic bearing, based on the geometric constraints of the contact between the top foil and the rotor and the overlap between the top foils, the mathematical model of the top foil structure of the bearing is established, and the key structural parameters of the top foil are solved by the parameter equation of the circle. The influence of the radius, thickness and number of top foil on the spread angle and installation angle of the bearing in the start-stop stage is analyzed. The results show that the expansion angle of the top foil increases first and then decreases with the increase of the radius of the top foil. With the increase of the thickness of the top foil, the maximum expansion angle of the top foil decreases gradually and the variation range of the expansion angle decreases by 12.4 %. The top foil spreading angle decreases with the increase of the top foil thickness, and the larger the top foil radius is, the more sensitive the top foil spreading angle is to the change of the top foil thickness. The installation angle increases parabolically with the increase of the top foil radius, and decreases linearly with the increase of the top foil thickness. The increase in the number of top foils will reduce the angle of the top foil, but will not affect the installation angle.