Resin transfer molding (RTM) is a very important category of low cost fibre reinforcement composite material manufacturing technique. But void which mainly formed at the process of filling and infiltration is able to reduce the performance of products. This paper first introduced how harmful the void is, and then formation theory, finally focus on the technical feature and resent evolution. Numerical simulation is always a mature and efficient research method for this field of investigation. Formerly, scientists also attribute their effort to such investigation, but, at that time, their simulation was 1D or 2D which can not represent the process accurately enough. Therefore the results are not so significant. Recently most studies pay attention to 3D simulation and how factors (such as injection pressure, structure of preform and so on) work. With the development of mathematic theory and simulation software some new numerical simulation methods present itself. Researchers may copy the course of resin’s filling in RTM more integrity to make their relation close to reality. Based on their achievement, the technique of RTM also improved to eliminate void’s emergence. However the real flow of resin is more than complex, more work should be done to avoid it and then set up a controllable industrial production system.