Abstract: The diffuser of mine's main ventilator is a device to reduce kinetic pressure at outlet,raise static pressure of ventilator and recover kinetic energy at outlet.Based on theory of fluid dynamics,the flow field and velocity field of 60°slant diffuser and streamlined type diffuser are simulated.The results of simulation can be used as guideline for selection of optimum parameters of diffuser to achieve good ventilation performance and reduce power consumption.