The cam profile and piston head shape of a TPFI engine were redesigned and the TPFI engine was modified into a Millercycle engine with compression ratio of 12.5. The influences of different compression ratios, oil pump structure and CLPEGR technology on combustion characteristics and thermal efficiency were further investigated. The bench test and simulation results show that the brake specific fuel consumption rate of optimal fullload operation conditions reduces from 238.6 g/（kW·h） to 226.5 g/（kW·h）. Besides, the thermal efficiency is up to 37.2% and the fuel economy improved by 5.07%．Meanwhile, the simulation is conducted by Cruise modeling and setting appropriate vehicle parameters and then the simulation results of fuel consumption under the two typical cycling conditions were acquired. Miller cycle engine saves fuel by 4.4% and 4.2% in NEDC and CLTC legislation condition respectively compared to the original engine, which has good engineering application value.