This　paper　studies　the　applications　of　Morlet　continuous　wavelet　transform　coefficients　method　on　feature　extraction　and　fault　diagnosis　of　diesel　engine＇s　abnormal　sound　faults.　Through　the　transform　coefficients　of　the　vibrant　signals　of　EQ6BT　diesel　engine＇s　piston　knock　and　piston　pin　knock,　a　scale-power　spectrum　plot　and　a　3D　power　spectrum　plot　are　obtained,　and　the　characteristic　of　these　two　spectrum　plots　can　be　used　for　classification.　With　this　approach,　feature　extraction　and　fault　diagnosis　of　diesel　engine　are　made.　The　result　shows　that,　by　using　the　scale-power　spectrum　plot　and　the　3D　power　spectrum　plot,　the　piston　knock　faults　and　piston　pin　knock　faults　can　be　detected　and　distinguished　directly　and　effectively.　Moreover,　the　degrees　of　faults　can　also　be　detected.