Bonnet polishing is a practical and economical polishing technology for the fabrication of precision optical components. Its removal function is controlled by many parameters, and much research has been performed on them in the past few years. However, most of the previous research has been focused on the inner pressure of the bonnet, the rotation speed of the spindle, the precession angle, the bonnet decrement, etc. The deformation of the bonnet under the inner pressure has received relatively little attention. This paper demonstrates the deformation of the bonnet under the inner pressure and its effect to the contact area and the bonnet decrement. It also proposes two solutions, one is to add an enhancement layer on the bonnet; the other is to design a novel bonnet contour which is aspheric but turns to spherical under the effect of the inner pressure. The latter one is proved that it's effective to reduce the deformation to the polishing process.