A fiber reinforced polymer composite deck module is used to form a deck constructed by assembling the deck modules. The deck module comprising an upper plate having an upper extension at its one side, a lower plate having a lower extension at its one side opposite to the side of the upper plate, and an interlink plate therebetween, forming therein a plurality of divisional portions of polygonal tubular cross-sectional shape, wherein at one side, including a first interlocking piece protruded downward at the end of the extension of the upper plate and a second interlocking piece protruded downward at a lower outer surface of the interlink plate, and at the other side, including a third interlocking piece protruded upward at an upper outer surface of the interlink plate and a fourth interlocking piece protruded upward at the end of the extension of the lower plate, wherein upon assembling the deck modules with each other, the first and second interlocking pieces of one module are detachably and mechanically snap-fit coupled to the third and fourth interlocking pieces, respectively, of the other module, and wherein the interlocking pieces coupled to each other have protrusions with a shape corresponding to each other for mutual mechanical engagement so that neighboring deck modules are detachably and mechanically snap-fit coupled in a vertical direction to each other to form a deck.