The invention relates to a horizontal pipe primary cooler leakage inspection method. The method includes the following steps of: leakage point locating for the lower sections of primary coolers; leakage point locating for the upper sections of the primary coolers; and leakage point locating for the tube bundles of the primary coolers. When judgment is performed on the lower sections of the primary coolers, the lower-section condensate liquid pumps of the primary coolers are turned off, so that the lower-section condensate liquid and cleaning ammonia of each primary cooler are closed; the rates of the incoming flows of the lower-section water seal tanks of the lower sections of the primary coolers are observed, a primary cooler of which the incoming flow rate is the largest is a leakage primary cooler; and the cold gas outlet valve of the primary cooler is turned off, and at the same time, the lower-section low-temperature water of the primary cooler is emptied, and the condition of the incoming flow of the lower-section water seal tank is observed, if no flows come from the lower-section water seal tank, it is confirmed that leakage exists on the lower section of the primary cooler. With the horizontal pipe primary cooler leakage inspection method of the invention adopted, thorough leakage inspection can be realized, the repair period of the primary cooler can be shortened, the leakage positions of one section of the primary cooler can be all found out at one time, leakage inspection time can be greatly saved, economic benefits are significant, and security risks are greatly reduced.