After removing the long-term tendency, cyclical fluctuating and seasonal fluctuating one by one from Baltic Freight Index, a null means stationary series is reached which matched ARMA model.

• 对波罗的海运价指数分别提取长期趋势项、周期波动项和季节波动项以后，得到了一个符合ARMA模型建模要求的零均值平稳序列。