This paper addresses how to predict the releasing and the deploying behaviors of the creased space membrane accurately. Although conventional study analyzed the released shape of creased membrane considering the elasto-plastic properties, that shape did not agree with the experimental results when the membrane is tightly creased. To examine the released shape of the membrane, at first, creasing and releasing experiments are carried out. The experimental results indicate that the opening angle of the crease increases with increasing elapsed time after releasing due to stress relaxation. The stress relaxation behavior is predicted by FEA considering on the visco-elasto-plastic material properties. In addition, the analytical model of the releasing and the deploying membrane is proposed. The results of the FEA and the analytical model show that the released angles are good agreement with experimental results. Thus, it is found that the effects of the viscosity are important to predict the releasing behavior of the space membrane.