Abstract: Based on guide wetting mechanism of low melting point alloy, a Cu-P brazing sheet coated with low melting point Ag alloy was prepared, the interfacial reaction mechanisms and properties of the 45 steel joint brazed using the sheet were studied and compared with that brazed joint using common Cu-P brazing alloy. The results revealed that the Ag alloy coating melts before melting of the CuP alloy and wets and reacts with the steel substrate firstly; then the Cu-P alloy melts and fuse with the Ag alloy, forms high-quality metallurgical bonding. The interfacial compounds layer at the joint brazed using Ag alloy coated sheet is far thinner than that brazed with common Cu-P alloy. The shear strength is higher than 160 MPa, the joint fracture inside the braze alloy close to the joint interface, and the strength and toughness are obviously improved.