The dispersion of a broadband optical parametric chirped pulses amplification (OPCPA) laser system is investigated. Using the numerical method, the theoretical model of dispersion and the effects of high-order dispersion on the charateristics in temporal and frequency domain of signal pulses are presented in broadband OPCPA laser system. The results demonstrate that dispersion induced by the pulse stretcher and phase change of signal pulses in the amplifier is relatively great, but the dispersion of parametric crystal can be ignored. The pulse duration is mainly controlled by the second-order dispersion, and the pulse signal-noise-ratio and waveform affected by third-order dispersion and fourth-order dispersion. However, the change of pulse frequency from dispersion is negligible.