The invention relates to prefabricated and combined porous floating breakwater suitable for long waves. The breakwater can be arranged in harbors, coasts, rivers and the like. Multiple energy dissipation mechanisms such as reflection resistance, energy peak dissipation, turbulence energy consumption, porous seepage energy consumption and the like are adopted. The floating breakwater consists of three parts, namely, floating components, mooring systems and connecting devices between adjacent floating components. The problems that existing breakwaters are complex in construction method, long in construction period and high in engineering cost are solved. Another technical scheme of the breakwater is as follows: in order to realize a better wave dissipation effect, water surfaces of the floating components are set as vertical still water surfaces, a plurality of wave-dissipation through holes are formed in wave surfaces and back surfaces, and grooves are formed in upper surfaces of the floating components, so that the wave energy can be consumed effectively, and the wave height behind the breakwater can be reduced. The breakwater adopts a thin-wall reinforced concrete structure and is high in self-strength; fixing seams are connected into a whole, and the firmness is good; the construction operation is convenient, short in period and high in efficiency; vertical construction can be performed in water surfaces of embankments of canals, ponds, rivers, lakes, seas and the like as well as waters, the foundation earth volume is small, the paving area is small, and the engineering cost is low.