The fault of a 6 cylinder high power density diesel engine during the bench verification of design was analyzed based on spectrum and ferrography methods.The correlation of the worn metal elements of Al,Fe,Cr and Mn was determined,as well as worn metal elements of Cu,Pb and Ni.The oil sample in which the Al mass fraction was increased abruptly by spectrum analysis was analyzed with the ferrography method,the large aluminum particles were found in the oil sample.With reference to the designed material of the engine friction pairs,the piston fault was determined and was further verified by the disassembly of engine.The accuracy and feasibility of fault diagnosis by oil analysis is improved with spectrum and ferrography methods,it is helpful for the accurate determination of the fault location of diesel engine.