Abstract: It is analyzed why sand-removing effect of conventional cyclone desander is bad,and it is pointed out that the column of whirling gas in the center has a marked effect on purifying mud.According to the analysis,we improved conventional cyclone desander.The improvement is that a round pole whose diameter equals to the diameter of whirling gas column is installed in the axes of conventional cyclone desander,which conduces to separating sand of inner cyclone and reduces swing range of inner cyclone and whirling gas column in order to enhance desanding efficiency.The experimental results show that the total desanding efficiency of the improved cyclone desander is 91%.