Abstract A new method of drawing the potential energy surface has been devised and compared with Eyring’s semi-empirical method. The points different from the latter method are that an appropriate function for the anti-bonding state of a diatomic molecule is assumed and the overlap integral is not ignored. The so-called Coulomb fraction in Eyring’s method is not used and the London equation has been slightly modified. As an example the activation energy of hydrogen atom-molecule reaction has been calculated. So far as this reaction is concerned, the present method gives more reasonable value than Eyring’s method.