The invention relates to a composite fertilizer production system, which comprises a gas outlet pipe, wherein the gas outlet pipe is unidirectionally wound with a heating pipe from one end of the gasoutlet pipe to the other end, the outer side of the gas outlet pipe is sleeved with a water conveying pipe, the water inlet of the heating pipe and the water inlet of the water conveying pipe are communicated to a water supply box, the water outlet of the heating pipe and the water outlet of the water conveying pipe are communicated to a thermal insulation water storage box, the water flowing directions in the heating pipe and the water conveying pipe are opposite to the tail gas flowing direction in the gas outlet pipe, the gas outlet pipe comprises a pipe body, the side wall of the pipe bodyis provided with fins at intervals, the fin is hollow, the interior of the fin is communicated to the interior of the pipe body, the inner wall of the pipe wall of the water conveying pipe is provided with flow separation plates at intervals, an annular water flow chamber is formed between the water conveying pipe and the gas outlet pipe, the flow separation plates and the fins are arranged in astaggered manner, and are annular, and a water flowing channel is formed between the flow separation plates and the fins. With the composite fertilizer production system of the present invention, thetail gas waste heat is completely recovered, and the flue gas is purified.