For the past few days, I have been studing the mechanical behaviors of accordion shape folded structures. I have also been studying the science of paper sheet, which is quite complicated. I have developed a mathematical model to predict the in-plane stiffness of both single-layered accordion shape folded structures and double-layered accordion shape folded structures, though part of the model is still under investgration. I have also made plans for further experiments to validate the model.