Abstract: In order to meet the need of carrying cuttings in annular space and make hole cleaned sufficiently,it is very important for studying on the ability of mud pump.According to the theory of drilling hydraulics,prediction model for mud pump was established on the basis of ensuring minimum flow rate. According to this model and the conditions of extended-reach well B3ERW4 in Liuhua oilfield,mud pump pressure and mud pump power were calculated on the basis of ensuring minimum flow rate which was needed to make hole cleaned sufficiently in every depth section.At the same time,the ability of mud pump which was actually used in Liuhua oilfield(i.e.Type 12-P-160 mud pump)was verified.Research results indicate that Type 12-P-160 mud pump do not meet the need of hole cleaning for extended-reach wells and at the same time this results provide scientific data for selecting mud pump rationally for the next step.