The amount of waste plastic generated due to increased plastic production and disposal is increasing, which is causing soil and marine pollution and climate change problems. To solve these problems, chemical recycling through pyrolysis emulsification is attracting attention as the most efficient method in terms of adding value and reducing waste through fuel and raw material conversion. In particular, polystyrene has the advantage of having the highest oil production during thermal decomposition because it is composed of only styrene. In this study, pyrolysis of waste EPS among polystyrene was performed using a semi-batch reactor implemented similarly to a continuous pyrolysis process, and oil yields were compared by changing sample type, nitrogen flow rate, and temperature conditions. As a result of this experiment, the optimal conditions (nitrogen flow rate 300 ml/min, WEPS, 380 °C) were calculated. In other words, the maximum oil yield (95.55%) was shown at 380 °C, which was selected as the optimal conditions for the EPS continuous pyrolysis emulsification system.