A pair approximation model is established to study the effect of the susceptible host's movement on hostparasite interactions. Disease-free equilibrium and endemic equilibrium are obtained by theoretical analysis. Through the discussion of local asymptotic stability of disease-free equilibrium by the Ｒouth-Hurwits, the critical value is obtained so that the infection is established. In addition, the corresponding computer simulation is given by Matlab. The conclusion has found some important phenomena and enriched the mathematical theory of infectious diseases.