Abstract: Compared with the conventional cementing,some technical control indicators of small annular clearance cementing operation has changed,and it makes the borehole pressure balance and cement rheological design index be affected by different degree.At present,small annular clearance cementing is treated according to the conventional well standards and it will result in unfavorable influence on cementing quality and construction safety.Therefore,the identification method and the cementing flow calculation method of small annular clearance have been studied,and the conventional method has been amended.By using the new method after amendment,by taking S well as an example,the application shows the results agrees with the experimental data very well.