The gears-cover was the main noise source of the ZH1130 single cylinder diesel. The critical modal was got using the modal analysis method combined with the frequency signal analysis, and then the ribs redesign was carried on using the topology method. The objective was the frequency maximum of the 1st modal; the constraint was the mass, and the variable was the design area. After the optimization, the 1st modal frequency increases by 241Hz. Finally, the experiment on the new gears-cover was operated, and the results show that the vibration velocity of the new design reduces in several critical frequency ranges and the SPL on 7th point reduces by 1.2dBA.