A 20 nm SiC nanocoating was prepared on the surface of crushed diamond particles using a combination of sol-gel and in situ reaction methods. 50 vol% SiC-coated diamond particles reinforced 6061Al composites were fabricated by vacuum hot pressing method. Part of the SiC, with a crystallographic orientation relationship of (-11-1)Diamond//(-11-1)SiC and [-110]Diamond//[-110]SiC between SiC and diamond, remains at the interface, which reduces the mismatch of phonon vibration modes between the diamond and Al matrix. Thus, the interfacial thermal conductance of the composite was greatly improved compared to that of composite prepared by diamond without coating. The thermal conductivity of the composite is 485 W/mK, which is the highest among the crushed diamond/Al composites and similar to that composite fabricated by single-crystal diamond. It is significant for the industrial application of diamond/Al composites that obtain a composite with well machinability and TC using the crushed diamond with nano-SiC coating.