The invention relates to an air cooler utilizing afterheat, which comprises an upper tube box (1), a cylinder body (2), a heat exchange tube bundle (3) and a lower tube box (5), wherein the upper tube box (1) and the lower tube box (5) are arranged at the upper and the lower ends of the cylinder body (2), the cylinder body (2) is divided into two sections, namely, an upper cylinder body (2.1) and a lower cylinder body (2.2), the upper cylinder body (2.1) is the high temperature zone, the lower cylinder body (2.2) is the low temperature zone, an air inlet (N1) is arranged on the cylinder wall of the upper cylinder body (2.1), an air outlet (N2) is arranged on the cylinder wall of the lower cylinder body (2.2), a cooled water inlet (N6) and a cooled water outlet (N5) are arranged on the cylinder wall of the lower cylinder body (2.2) from bottom up, a 1# valve is arranged at the cooled water outlet (N5), a heating backwater inlet (N4) and a hot water / cooled water outlet (N3) are arranged on the cylinder wall from bottom up, a 3# valve is arranged at the hot water / cooled water outlet (N3), and the cooled water outlet (N5) on the cylinder wall of the lower cylinder body (2.2) is communicated with the hot water / cooled water outlet (N3) on the cylinder wall of the upper cylinder body (2.1) through a 2# valve. During the operation of the air cooler utilizing afterheat of the invention, not only the gas can be cooled, but also the heat energy can be extracted to generate hot water.