The screening of the logistics forecasting indices is the first step of a logistics demand forecast.Based on the analysis of the port throughput and its influential indices, we propose a series of screening principles and methods. Taking the ports in the North Gulf of Guangxi as an example, applying the Grey Relational Analysis method and DPS（data processing software）tool, we find the correlations between the port throughput in the North Gulf of Guangxi and related forecast indicators based on the data from 2000 to 2008.Finally, a group of well-constructed indices highly correlated are chosen as the final port throughput forecasting indicators.