The hydraulic system operating principles for high pressure roller mill were introduced. Based on classical control theory, a mathematical model for this system was established in the style of transfer function. With the software Matlab, the dynamic characteristics of the system were analysed through system emulation. By studying the system responses to three kinds of input signals, the flow coefficient K has tremendous influence on the system dynamic characteristics. If the coefficient K is oversize, the system oscillates. The hydraulic pressure p0 of accumulator affects the displacement x of the roller. The higher the pressure p0, the more displacement x of the roller.