An appropriate design of the inlet type has been proved to be an effective approach to improve the performance of a hydrocyclone. Until now, there is still no detail analysis on the mechanism underlying the flow control by the inlet type. In this paper, numerical simulation was conducted to investigate effects of curvature radius on the separation performance of the hydrocydone with a tangent-circle inlet The validity of the approach was verified by the reasonably good agreement between the predicted and measured results in terms of water velocities and particle partition curves. The simulating results were further analyzed in aspects of the flow field, pressure drop and separation performance. Results showed that a smaller curvature radius could increase the tangential velocity and the pressure gradient. Besides, the turbulence kinetic energy in the inlet section and the annular section are reduced by decreasing the curvature radius. Meanwhile, the symmetry of the inner flow field was improved by reducing the curvature radius. All these factors enhanced the radial regular distribution of parades in the inlet section and reduced influences of the short circuit flow on relatively coarse particles. Therefore, the classification precision was improved when using a tangent-circle inlet with a smaller curvature radius compared with base hydrocyclone. (C) 2016 Elsevier B.V. All rights reserved.