Abstract: CNOOC uses e-Drilling software to perform real-time simulation of wellbore cleaning, and the calculation results of this software have low accuracy. In order to improve the accuracy of borehole cleaning calculation, a new method for borehole cleaning calculation has been explored. By calculating the critical flow rate required for the suspension of cuttings in the annulus and the flow rate of the drilling fluid in the annulus, the critical flow rate and the flow rate of the drilling fluid are compared to determine the thickness of the cuttings bed, and then calculate the concentration of cuttings in the annulus and the wellbore ECD (equivalent circulating density). The new method has been used to calculate two extended reach wells in Area A. Compared with calculated results of the e-Drilling software and measured ECD values, the results show that the accuracy of calculation with the new method is improved obviously. The practice shows that this method has higher technical value.