Abstract: Steady-state simulation including the impeller, vaneless diffuser and volute with different configurations of inlet pipe was carried out to investigate the effects of inlet pipe on the compressor performance.The results show that the uncorrelated performance curve varies obviously with different inlet pipes.When the inlet pipe is longer in length or smaller in diameter, the pressure ratio and choked mass flow of the compressor become smaller.It is because the existence of inlet pipe changes the incidence angle at the impeller inlet which determines the performance of the compressor.If compared by correlated performance, the influence of the inlet pipe is relatively smaller.However, the correlated choked mass flow is still smaller when the inlet pipe is longer in length or smaller in diameter.