On the basis of laboratory investigation, 9 types of Al-basic sacrificial anodes with different compositions are selected and studied in the harbour. Anodic closed circuit potential and output currents are also measured. Anodic surface resolved characteristics are recorded in detail at the end of experiment. Current efficiencies and discharge capacities of anodes are calculated. Environment factors: temperature，conductivity, pH and salinity of sea water are measured too. It can be seen from the results that (1) properties of No. 1 anode are the best, next come Nos. 2,4,6,3,5,7,8,9 in that order. Nos. 1-6 anodes may be applied to protect marine constructions as anodic materials in marine engineering and their discharge capacities are 2-3 times as large as Mg-basic and Zn-basic anodes; (2) effect of alloy element In (indium) on anodic properties is evident, content of In being controlled at about 0.024%. If content of In exceeds 0.03%, properties of anode deteriorate; (3) output currents are affected by anodic properties themself, also by temperature and conductivity of sea water. When temperature and conductivity come down, anodic output current decreaes.