The misplacement of coarse particles in overflow and fine particles in underflow are problems in hydrocyclone separation. This paper proposes improved feed body design of a hydrocyclone and the effect of feed body geometry on the flow field and separation performance is investigated experimentally and theoretically using PIV and CFD, respectively. The air core formation and the velocity field are in good agreement using both approaches. Further simulated results indicate that the tapered feed body causes a reduction in fines entrainment by underflow, suitable for fine particles classification. In contrast, the conical feed body is advantageous for eliminating short circuiting.