This paper is concerned with deformation analysis of diaphragm-type air springs, especially an air bag which consists of nylon fiber-reinforced rubber, composite rubber linings and steel wire bead parts. The analysis has been carried out with a finite element code developed to consider the orthotropic properties of fiber-reinforced rubber lamina, geometric nonlinearity by large deformation, and contact between an air bag and a bead ring. Five different models have been considered in the design optimization procedure in order to investigate the effect of design variables with the variation of the cord angle of an air bag. The analysis provides the hoop and the longitudinal strain distributions in an air bag as well as the variation of the outer diameter, the fold height and the vertical force with respect to the internal pressure.