The invention belongs to the technical field of machines, and relates to a spray coating device with a boat fender or navigation mark core body, in particular to the spray coating device for an on-water floating solid-core polyurea elastomer. The device is applied to spray coating occasions of the on-water floating solid-core polyurea elastomer, and solves the technical problems of large labor intensity of manual preparation, low efficiency and low standard degree of the product are solved; moreover, the production efficiency can be effectively improved, and the spray coating device is used for carrying out spray coating of large-scale buoyant boat fender products. The two ends of a machined body are firstly fixed; then a first support is moved to the right lower part of a spray coating machine along a first sliding rail; parameters of the spray coating machine are set, an air compressor is started and a variable frequency motor is started, and a second rotary shaft is driven by the variable frequency motor to rotate the machined body; a spray nozzle or a spray gun is opened to carry out spray coating until the spray coating procedure is completed. The device has a simple overall structure, is reliable in principle, is high in production efficiency, is convenient to operate, is low in labor intensity, is high in standardization degree of the product, is good in quality, is friendly in environment, and has good economical benefit and wide market prospect.