Abstract: Numerical simulation was carried out by using fluid Volume function（VOF） method to study the equal-sized head-on binary droplet collision in steam separators. The typical coalescence and reflexive separation with low, middle, high We, were investigated. Droplet shapes during the collision process were observed. And transformation between kinetic energy and surface energy, energy dissipation were analyzed to achieve better knowledge on the collision process. It was found that in high We reflexive separation, the external liquid departures out of the droplet and forms a circular ring. The liquid ring is forced by the surface tension to contract and impact on the inner liquid, which leads to the surface’s fierce and complicated oscillation. This phenomenon affects the separation process and satellite droplet formation. And Kim’s satellite droplet model cannot make precise prediction. By simulating the equal-sized head-on collisions with various We, critical We between coalescence and reflexive separation was found as 15.6. And comparison with three models shows that, Qian model matches well.