Staged fracturing of horizontal wells is an essential development technology for lowpermeability gas reservoirs, and the stage interval will affect fracturing treatment and production rate greatly. Different from the previous reservoir simulation method, the optimal design method in this paper is based on the production of frac-tured vertical well and experience to determine the stage spacing, and considers both production and stress distur-bance. As a prerequisite, the productivity of horizontal well should be equal to the open well's at the least, at the meaning while, assuming that gas flows linearly from formation into fractures, and enters the wellbore radially, the calculation equation is derived to determine the max stage interval. The minimum stage interval can be calculated by stress disturbance theory around fractures. At last, the two calculation methods are combined to define the maximum and minimum scope of stage interval. A computation case shows that the optimal method is optional for on-site rapid fracturing design.