The composition of fouling organism's community was on-spot detected on several portions below waterline, including the bow, hull and stern rudder bay, of the so called “Seagull floating dock”, which has been in service for more than 5 years at Qingdao harbor. It is found that more than 30 species of eight types of organisms were detected, among which Mytilus galloprovincialis is the dominant species, and it is the first time that the Scrupocellaria species was discovered in this area. The ranking of species diversity is bow > stern rudder bay>hull. The most seriously fouling portion is the stern rudder bay, where the fouling organisms here overlap and attach to a thickness up to 15 cm, and the percentage of covered area of the hard-shelled fouling organisms reached 70%. The influence of seasonal factors, hull structure, sea current state and sunniness on the fouling organism's community was discussed. The on-the-spot classification method was proposed for the first time and applied in this study, the fouling organisms detected on the Seagull floating dock were classified into four categories: hard-shelled groups, crusting groups, uprighting groups, and algae groups. Then the biofouling distribution map of the floating dock was drawn according to the size of the attachment area of the hard-shelled groups. This can promote the communications between the non-biological professionals, the formulation of anti-fouling standards, and the mathematical modeling of fouling organisms.