The present invention relates to a composite metal material and a low-temperature solder paste with high thermal conductivity containing the same. The composite metal material is a Cu core/Ag intermediate layer/Sn shell type metal powder (Cu@Ag@Sn) or a Cu core/Ni intermediate layer/Sn shell type metal powder (Cu@Ni@Sn) with a particle size of 20-60 μm. The low-temperature solder paste with high thermal conductivity is obtained by mixing the composite metal material with an Sn—Bi series alloy powder and a flux paste, can be used for welding of a variety of substrate, and is suitable for welding at a low temperature of lower than 150° C. The composite metal material of the present invention has a simple process, a low cost and high practicability, and poor heat dissipation and other problems of power devices after die bonding caused by low thermal conductivity of current solder pastes on the market are solved.