The invention belongs to the technical field of air traffic control radars, and particularly relates to a harmonic filter for an air traffic control primary radar. The filter comprises a middle pipe,wherein an inlet hole and an outlet hole are respectively formed in two end plates of the middle pipe; coupling holes are formed in all side plates of the middle pipe in a penetrating mode, the coupling holes in the upper side plate and the lower side plate are in one row to form a single-row integrated coupling plate, and the coupling holes in the left side plate and the right side plate are in two rows to form a double-row integrated coupling plate. The filter also comprises a single-row branch waveguide and a double-row branch waveguide. A cross-shaped structure is formed between each branch waveguide and the middle tube; the filter further comprises wave-absorbing load pins, and each wave-absorbing load pin and each group of coupling holes form a one-to-one correspondence relation. Onthe premise of ensuring the initial use function, the structure of the harmonic filter is simplified, the processing cost is reduced, the processing period can be remarkably shortened, and the industrial batch production requirement can be met.