Homogeneous Charge Induced Ignition (HCII) combustion can achieve low emissions and high efficiency. However, the gasoline ratio of HCII combustion at medium and high load is limited by rough combustion. In this paper, a lower compression ratio was utilized to relieve the rough combustion at medium and high load. This strategy was verified by experiments on a heavy-duty multi-cylinder engine. It was found that by reducing the compression ratio from 18 to 16 the peak in-cylinder pressure was effectively reduced and the gasoline ratio range could be obviously extended. Thus, the combustion and emission characteristics of HCII at medium and high load was noticeably improved. The reduction of soot emissions at specific operating conditions could be close to 50%. The results in this paper also have reference value for other dual fuel engines.