The stability of ballast is the key to guarantee the traffic safety. This paper is on the back -ground of ballast settlement monitoring of a bridge constructed by jacking method. And the bridge is located at the 1094 kilometers in Jingha railway line. Monitoring data is analyzed by the time series method. Then we build an ARIMA model for these data. Through the AIC principle, the orders of the model are obtained. Then we predict the settlement of the ballast. By the comparison of predictive value and the true monitoring data, it shows that using time series to analyze the settlement of ballast is reasonable and reliable. Therefore it is a new method to analyze the settlement of ballast. At the same time, this method only relay on the monitoring dates but not on other conditions.