Abstract: The space of discontinuities is one of important indexes which explains the distribution of discontinuities and also classifies quality of engineering rock mass.Unlike the traditional definition of discontinuities space,this paper points out that the distribution of discontinuities can be analyzed as long as the spaces of neighboring discontinuities are measured.It presents the four-type methods of classifying discontinuities to built the discontinuities series.It set up an ARIMA model of discontinuities space by means of theory of time series and provided methods of building and checking model.An actual case is studies to show that the ARIMA model is suitable.