Abstract: To study influence of Ni-P coating thickness on mechanical properties of Cu/Al brazed joints, Zn98Al brazing filler metal was used to braze T2 copper with different coating thickness and 3003 aluminum alloy, and a series of brazed joints were obtained. Spreading wettability of brazing filler metal on coated copper plate was studied. Microstructure morphology of interface on Cu side, thickness and type of compound layer were analyzed by optical microscope and scanning electron microscope, and influence of coating thickness on mechanical properties and fracture morphology of brazed joints was further studied. The results showed that with the increase of coating thickness, spreading area of brazing filler metal on coated copper plate increased first and then decreased. Compared with uncoated copper plate, when coating thickness was 5～20 μm, spreading area of brazing filler metal increased nearly 3 times from 62.4 mm² to 189.5 mm². In this case, spreading area of brazing filler metal was stable and wettability was better, which was conducive to obtaining well joints. Compared with uncoated brazed joints, when coating thickness was less than 5 μm, structure at the Cu-side interface was still coarse Cu_3.2Zn_4.2Al_0.7 compound layer, and shear strength of brazed joints had little change. When coating thickness was 5～20 μm, the coating could effectively prevent diffusion of Cu and Al atoms, and structure at the Cu-side interface of brazed joints changed into Ni-P coating and thinner Al₃Ni compound layer. Meanwhile, shear strength of brazed joints increased to the maximum 39 MPa, which was about 21.8% higher than that of uncoated brazed joints. When coating thickness was more than 20 μm, structure at the Cu-side interface of brazed joints changed into irregular Ni-P and Al₃Ni compound layer, and shear strength of brazed joints began to decrease sharply. Considering spreading wettability of brazing filler metal, structure at the Cu-side interface of brazed joints and mechanical properties of brazed joints, the optimum thickness of Ni-P coating was determined to be 5～20 μm.