To enhance the operating performance of an off road diesel engine in plateau conditions，the engine power

fuel consumption and emission characteristics working at different conditions and altitudes were studied by a bench test. Then the simulations with GT-POWER software were carried out to understand the impacts of altitude on the operation characteristics of turbocharging system. The mechanisms of performance deterioration at high altitude conditions were analyzed in detail. Aiming to the performance recovery of diesel engine at high altitudes

a regulated two stage turbocharging system with exhaust bypass valve was matched with the engine through the parameters calculation. The research results showed that altitude significantly affected the performance of the off road diesel engine. At the engine speeds between 800r/min and 2800r/min

a significant reduction in engine torque and a very important increase in the brake specific fuel consumption (BSFC) were achieved with the rise of altitudes. As the altitude increased from 0 m to 2000m

the engine power dropped as much as more than 4.3%

and the BSFC increased as much as more than 6%. At high altitude conditions

the intake manifold boost pressure and the exhaust manifold pressure both declined sharply while the intake and exhaust manifold temperatures both increased

and the emissions of total hydrocarbon (THC)

carbon monoxide (CO) and nitrogen oxide (NOx) increased remarkably. Compared to the single stage turbocharging

the engine power was improved by 14.9% and the brake specific fuel consumption was reduced by 11.8% at 4000m altitude with a regulated two stage turbocharging system. A method of optimized turbocharged diesel engine matching for altitude adaptability was obtained.