A novel two-stage Laval annular mechanical foam breaker was designed which primarily uses the vacuum generated by the Coanda effect and the Laval principle to break foam. The value and the distribution of the negative pressure inside the foam breaker are very important to its performance. Here, we employ the computational fluid dynamics (CFD) code FLUENT to simulate the flow characteristics inside the foam breaker. The simulation results showed that the maximum velocity and negative pressure which generated in nearby the second throat plane is about 520m/s and -62kpa,respectively. The range of the internal negative pressure is larger than that of the others when the angle of the first diffuser is 0 and the annular slit distance is 150 mm.