The purpose of this study is to analyze the effect of contact pressure on the contact pressure distribution, contact deformation and airtightness generated at the contact surface of bolts fastened by the analytical method for the sealed structure of fastening bolt. In this paper, as a first step, we investigated the characteristics for magnitude and distribution area of contact pressure with respect to the separated distance from bolt center according to the flange bolt size and tightening torque by structural analysis. The sizes of flange bolt were M6, M8, M10 and M12, and the tightening torques were applied with the minimum, intermediate and maximum values according to the size of each flange bolt. As a result, in the same flange bolt, the larger the tightening torque, the larger the surface pressure with respect to the same separated distance from bolt center, and the greater the distribution region slope of contact pressure, but converged to near a value less than the contact pressure of 1 MPa.