Compared with the diesel engine with variable nozzle turbocharger, the performance and economy characteristics of diesel engine without variable nozzle turbocharger are experimentally investigated under various operating conditions in this paper. The diesel engine with variable nozzle turbocharger is employed to evaluate the effects of the opening degree on supercharging pressure, air flow, brake specific fuel consumption, smoke intensity and exhaust temperature of diesel engine. And the external and universal characteristics of diesel engines are also studied. The result shows that the variable nozzle turbocharger is beneficial to improve the performance and economy characteristics of diesel engine at the speed range of 900-1300 r/min. The experiments were carried out on the urban bus in Hezhou Road located in Guangxi Province (China) with engine of the YC6J200-42 series. The variable nozzle turbocharger can significantly optimize the performance and economy characteristics of whole vehicle, especially at low and medium speeds with lower smoke and nitrogen oxide emissions. Owing to the research data, the opening degree of variable nozzle turbocharger should be adjusted as much as possible to reduce the exhaust back pressure and pumping loss to improve the fuel economy of the engine.