The elastomeric O-ring is used as a packing element in the diverse parts of industrial system, such as the high pressure vessel, the oil supply equipment, the aerospace component, and the nuclear power plant etc. The design criterion of O-ring was determined by analyzed results of stress and the deforming behavior at various loading conditions related with sealing pressure and fit condition. The shape of O-ring was changed according to the squeeze rate, the sealing pressure, and time. At last, the study of deforming behavior and distribution of internal stress distribution from the constant squeezing O-ring with various sealing pressures was carried out on the real-time observation. To realize the experimental progress, we developed a specific loading device for the hybrid transmission photoelasticity under the continuous applying of the sealing pressure for squeeze rate. The O-ring was infiltrated into the space gap between the low-sidewall and the front-sidewall while the test load was forcing out. The analysis using the photoelastic model experiment of interior stress field in the constant squeezing of O-ring seal evidently gave a solution to predict the characteristic fracture of elastomeric sealing material.