Abstract: The theoretical analysis and experimental verification about the elastic properties of Plain Weave Fabric Composites (PWFC) is discussed in this article.Representative Volume Element (RVE) method is used to predict the elastic properties according to those of raw materials of PWFC. RVE method belongs to micromechanics, in which an element that can represent the properties of the whole material is selected and studied, thus the contribution of fiber, resin, interface can be analyzed respectively. The simplest unit cell of PWFC is taken out as RVE in this research. A mathematics model based on RVE is set up and the yarn shape in the composites is regarded as sinusoidal. The relationship between micro structure and macro properties is analyzed. A predictor program is made for predicting quickly. The predictor software programmed with Visual Basic has some convenient features. With considering all factors of the yarn geometric shape, the fiber volume content and the hollow rate, the theoretically elastic data of PWFC can be predicted. Compared experiments are done by using lay-out and RTM process to make samples. The relatively small error between the experimental result and predicted data proves the feasibility of the mathematics model and predictor method.