The invention provides a glass fiber reinforced plastic septic tank. The septic tank comprises a septic tank body, and the septic tank body is composed of a sewage inlet, a dirt outlet and a tank body; and the sewage inlet and the dirt outlet are arranged at the left end and the right end of the tank body. Main raw materials for producing the septic tank include methyl benzoate, phthalic anhydride, glutaric acid, fumaric acid, castor oil, neopentyl glycol, styrene, methyl methacrylate, diallyl phthalate, a polymerization inhibitor, polyvinyl acetate, an inorganic filler, an antioxidant, a curing agent, an accelerator, glass fibers and a waste paper pulp. The glass fiber reinforced plastic material has good impact strength, good crack resistance and good corrosion resistance, and a ratio ofparticle with different diameters in the inorganic filler is controlled to make the inorganic filler well dispersed in the unsaturated polyester and effectively fill gaps among the fibers in order toimprove the compactness of the product, so the reinforcing effect of the filler on the material is improved.