In this paper, the properties of a slow exciton in a polar crystal are discussed. The previous work of the author is generalized to the case that the electron mass is not equal to the hole mass. A perturbation method developed by Haga is used. In the approxiamation that the interaction of phonons of different wave vector in the recoil effect can be neglected, the wave function in the second order approxiamation is derived, and the electrostatic pontential is also calculated.