The kinetic ballooning-mode eigenequation, which can be used to study the stability criterion in the second stability regime, is derived. It retains various most important kinetic effects. The corresponding form of this equation for circular tokamak is deduced to include the effects of the magnetic surface displacement and the poloidal magnetic field that become important in the second stability regime. The structures of the modes and the stability criteria for various configuration parameters are studied by using a numerical shooting code. Compared to the ideal MHD case, it is found that a new unstable branch of the mode exists in the second stability regime, having a very weak growth rate. In addition, there are several sorts of marginal stable modes, their behaviours have been studied to examine the effects of the magnetic shear and the poloidal magnetic fields.