A Weichai-WP12 heavy-duty diesel was taken as the research object and the influence on two-stage turbocharged system was researched, according to contrasting the two states of the IVCA which control mode was open or close. It was also analyzed that the effect on combustion process by key gas path parameters of diesel engines under each speed and middle load condition. The results show that the NOx and soot compromise exhaust emission was significantly declined by IVCA when the injection timing was delayed further after top dead center. At the same time, it was found that IVCA could decrease air intake flow and backpressure, and then it was considered as a useful way to improve the effective thermal efficiency when engines ran under high backpressure condition. The optimization matching process between boost system and IVCA under middle load working condition could come true if the influences of IVCA on operating principle of boost system were found , while the key air path parameters and fuel parameters was collaborated and controlled precisely.