Abstract: The environment pressure and air density experience sharp declines at high altitude, which cause a large drop in the intake air mass flow rate of diesel engines. As a result, many aspects of engine performance are deteriorated, such as power, fuel consumption and emissions. Turbocharging matching provides a good technical solution for recovery diesel engine performance at high altitude. There is a large number of agricultural machinery operating in plateau area of China. In order to ensure that the agricultural machinery used in these areas had a good plateau adaptability, taking a small agricultural diesel engine as the research object, an appropriate compressor and turbine were selected respectively through theoretical calculation according to the design and development goals at altitude of 2 000 m. After that, the matching test of the small agricultural diesel engine and selected turbocharger was conducted at this altitude. Finally, the simulation model of the small agricultural turbocharged diesel engine was built by using GT-Power code based on test data. The change rule of diesel engine key performance parameters were simulated and investigated at altitudes of 0, 2 000 and 4 000 m. The results showed that the selected turbocharger made the small agricultural diesel engine achieve the development requirements at the altitude of 2 000 m. Low-end torque reached 120.1 N·m at 1 000 r/min, the peak torque was 180.2 N·m at 1 600 r/min, the rated power was 37.4 kW at 2 600 r/min, and the torque backup coefficient was 131% at this altitude. At 3 altitudes of 0, 2 000 and 4 000 m, the joint operation lines of the small agricultural diesel engine and the selected compressor were all operating in the relatively high efficiency area, and there were a large surge margin at low engine speeds, and also a certain distance from the choke line at high engine speeds. As the altitude went up, the engine torque and boost pressure decreased, while brake specific fuel consumption and turbine inlet gas temperature increased. What's more, with respect to high engine speed, the change of altitude had a greater impact on engine power and economy performance at low engine speed. With the increase of altitude, decreasing amplitude of torque and percentage gain of fuel consumption was both rose at low engine speed, and these tendency were decline gradually with the increase of engine speed. In addition, the engine speed corresponding to the peak torque showed a tendency of gradually moving towards higher engine speed at high altitude. Compared with plain area, the maximum engine torque decreased by 2.59% and 7.19% respectively when it ran at altitudes of 2 000 and 4 000 m. Meanwhile, compared with the previous literatures conclusion, the decreasing amplitude of peak engine torque was smaller when the small agricultural diesel engine operating at altitudes of 2 000 and 4 000 m, respectively. It can ensure the good operation performance of diesel engine in plateau area, and also is beneficial to improve the plateau adaptability when diesel engine and turbocharger are matched at high altitude.