Abstract: Based on the concept of multi overflow pipe cyclone and combined with the study on cyclone column separator, a new type of separating and classifying two-stage cyclone device was designed.A part of the overflow flows directly from the upper overflow pipe, the other part flows from the side of the overflow outlet along the tangent line into the second section of the cyclone for again grading.The side overflow separation and classification through just one feed can achieve the goal of di scharging stones from the underflow of the first section, fine coal from the underflow of the second section and fine mud from overflow of the first section as well as the second section together at the same time. Taking the-3 mm coal slime of Majaliang Coal Preparation Plant as the research object, the insertion depth of overflow pipe a nd side overflow connection caliber studies were tested respectively.The results show that, the above test conditions have significant effects on the classification and se paration of the device.To ensure the effect of separation and classification of the device, the depth of the overflow pipe should not be more than the depth of the sleeve, and large connection caliber will cause the higher ash of the second underflow and decrease the classification performance of the second stage cyclone.