In order to research the effect of inlet aspect ratio on the velocity field, pressure drop and particles trajectory in⁃side a cyclone, the method of Computational Fluid Dynamics(CFD) was used for the simulation of five cyclones whose aspect ratio are 4:1、3:1、2:1、1.5:1 and 1:1 respectively. The simulated results verified by later experiments show that, under the condition of the same inlet equivalent diameter and feed speed, when the aspect ratio increases, the tangential velocity and radial velocity of the fluid increase apparently, which is beneficial for improving the separation accuracy. But when the aspect ratio is greater than 3, the increasing tendency is not apparent. Another conclusion is that the pressure drop increases and the separation size becomes smaller with the increment of the aspect ratio. In addition, the simulated trajectory of different size particles indicate that, if the as⁃pect ratio increases, the small particles can enter into the overflow more easily and the large particles can flow into the underflow more easily. From the above perspective, when the inlet aspect ratio is 3, the long and narrow inlet is more favorable for classifica⁃tion.%采用计算流体力学（CFD）方法对进料口长宽比为4：1、3：1、2：1、1.5：1、1：1的五种旋流器进行了模拟，研究进料口长宽比对旋流器内部的速度场、压降和颗粒运动轨迹的影响规律，并与实验结果进行了对比验证。结果表明：在相同的进口当量直径和进料速度条件下，增大进料口长宽比，流体的切向速度与径向速度明显增加，有利于提高分离精度，但当长宽比大于3时这一增加趋势变缓；随进料口长宽比的增大，压力降呈递增趋势，分离粒度变小；不同粒径颗粒的运动轨迹分布表明，增大进料口长宽比，可以有效减少底流夹细和溢流跑粗现象。从上述角度来看，当进料口长宽为3时，狭长型进料口更有利于分级。
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