Reasonable structural design for a inlet pipe is an important way of improving the hydrocyclone's separation performance. The inlet can not only guide and accelerate particles but also achieve pre-separation of particles. However, there still lacks of clear governing equation of ideal inlet pipe. In order to gain in-depth understanding of the effects of different structures of the inlet pipes on the inner flow field and separation performance of the hydrocydone, this study employed numerical simulation to compare the performances of the inlet pipe with different structures (linear, arc-type, spiral-line inlet pipe, denoted as Type A, Type B and Type C). Moreover, a novel hydrocyclone (Type D) mainly consisted of spiral-line inlet pipe, arc-type overflow pipe and parabolic cone was developed in this study. The simulation results fit well with classical experimental data, thereby validating the accuracy of the simulation results. Based on the simulation results, using Type B and Type C inlet pipe, both pressure drop and tangential velocity increased, which facilitated the movement of coarse particles towards the wall as well as finer particles towards the center. The pressure drop and the tangential velocity were greatest in Type C but lowest in Type D. The axial velocity of the internal rotational flow in a curved inlet pipe (especially Type D) was low, which can prolong the retention time of fine particles and contribute to more thorough separation. Using Type D inlet pipe, both the short-circuit flow rate and the turbulent viscosity were effectively lowered, which reduced the occurrence probability of eddy and enhanced the smoothness of particle movement. In addition, using spiral-line inlet pipe can promote the movement of coarse particles towards the wall, which significantly enhanced the recovery rate of coarse particles. Conclusively, Type D inlet pipe exhibited the highest separation precision and the lowest cut size, accompanied with better product quality. (C) 2020 Elsevier B.V. All rights reserved.