OpenStack is a cloud operating system, but it does not provide the predictive functionality for cloud disk usage of the virtual machines running on it. In this paper, it propose a prediction scheme of virtual machine cloud hard disk capacity. First the Libvirt API is used to obtain the disk data of the virtual machine. After data processing, the ARIMA time series model is built. Then the capacity of the disk in the future is predicted. This scheme can predict the disk capacity of virtual machine, facilitate the user to expand capacity or issue an alarm, and then reduce disk failure.