By using information entropy theory, the four kinds of structure pressure vessel''s allowable reliable coefficients of initial yield and burst intensity were analyzed under the harshest pressure test and the normal operation. Based on three kinds of failure criteria, such as yield, burst and fracture, from the equal-reliability viewpoints, the reliable index of pressure vessel is determined:1)for steel thinness wall cylinder, spherical vessel and flat ribbon-wound pressure vessel, the reliable index of initial yield intensity is equal to 1.920or 0.815during barometrical or hydraulic pressure tests, and equal to 3.189under the normal operation; 2)for steel thinness wall cylinder, spherical vessel, flat ribbon-wound pressure vessel and super-high pressure thick wall cylinder, the reliable index of initial burst intensity is equal to 4.729or 3.740during barometrical or hydraulic pressure tests, and equal to 6.828under the normal operation. The foundational question of pressure vessel probability safe evaluation is solved.