In this reported study, a new Q criterion was proposed to analyze the vortex in three cyclones that had various inlet structures. The Reynolds stress model (RSM) was used to simulate the gas flow, and the Phase Doppler Particle Analyzer (PDPA) was used to measure the fluid velocity. The results showed that the vortex structure was intuitive according to the new isovortex surface that was obtained using the Q criterion. The isovortex surface was found to be distorted and not distributed around the center axis. With the development of flow, the equivalent diameter of the isovortex surface gradually decreased. The magnitude of the vorticity and the vortex lines of axisymmetrical volute inlet (AVI) structure were more uniform and symmetrical than those found into the single tangential inlet (STI) structure and the single volute inlet (SVI) structure. (C) 2020 Published by Elsevier B.V.