In this paper, the effect of the lattice vibration on the exeiton motion is discussed by a perturbation method that was developed to investigate the problem of plarons by Haga. Our previous work is generalized to the case that the electron mass and the hole mass are not equal. When we neglect the interaction between phonons of different wave vector in the recoil process, the ground state energy, effeetive mass, reduced mass and inner potential energy are derived. It is shown that the effective mass of the exeiton depends on the interaction between the electron, hole and the phonons reduced mass of the exciton not only depends on the interaction between the electron. Hole and the phonons, but also on the electron and hole mass ratio; the formation of a self trapping exciton is not determined by the magnitude of the interaction between the electron, hole and the phnon, but by the electron and hole mass ratio. A exciton is self trapping when the electron and hole mass ratio is in the range 0.261 e/μh<3.83.