Two strategies were evaluated on a single-cylinder diesel engine to reduce the emissions and improve the thermal efficiency based on the mixing-controlled LTC. The high rates of cooled EGR were first introduced to decrease the in-cylinder combustion temperature by the traditional method. Retarding the intake valve closing angle was used to reduce the effective compression ratio by using Miller cycle. Low-temperature combustion was realized by further coupling with boost pressure. The results show that both high EGR rate and Miller cycle can reduce NO_x and soot emissions based on different mechanisms. High EGR rate decreases the combustion temperature to reduce NO_x and soot emissions. Miller cycle has little influence on the decrease of combustion temperature and hence the reduction of NO_x emission is less. But the large decrease of local equivalent ratio will reduce soot emission obviously. High EGR rate implies a sacrifice of combustion efficiency, the brake thermal efficiency (BTE) is determined by the ITEg and combustion efficiency. Miller cycle with a higher combustion efficiency has a good compromise between emission and efficiency and the smallest effective compression ratio as well. The too low effective compression ratio will lead to the high requirement of intake pressure, and BTE is determined by ITEg and pumping loss.