A GT-Power model was established to analyze the influence of intake and exhaust port heights on power and scavenging performances of an opposed piston two-stroke（OP2S) diesel engine. A multi-objective optimization method was used to optimize IMEP

scavenging efficiency and trapping ratio at different speeds and to evaluate the power and scavenging performance of the diesel engine. Results show that the optimal intake and exhaust port heights increase with a rise in speed

and compared with the fixed port height

the use of variable port height according to specific speed can increase IMEP. So using variable port height system to achieve VVT can greatly improve the comprehensive performance of the OP2S diesel engine.