To study the influence of different geometric parameters including the radius of shell, shell thickness and the crack length on the bulging factor, this paper calculates the bulging factors of unstiffened pressurized cylindrical shells with longitudinal crack by geometric nonlinear finite element analysis in ABAQUS, the numerical results of bulging factor are compared with existed empirical solutions, the effect of biaxial load on the bulging factors is also discussed. The results indicate that the bulging factor is influenced strongly by most of the geometric parameters; limitations on the use of empirical solutions do exist; Increasing biaxial load ratios from 0.5 to 1.0 reduces the bulging effect by 20%. Conversely, decreasing biaxial load ratios from 0.5 to 0 increases the bulging effect by 28%.