Abstract: The oilfield practice proves that in middle and later oil production periods，or in the ex-ploitation of deep，low一permeability reservoirs，it is an effective way to enhance oil recov-ery by incerasing the pump setting, depth. In the paper，the modified formula of calculating the pseudo一static load in a conventional straight well are applied to the calculation of the deep pumping load，and a theoretical modeling is derived for tapered rod string design in a
deep well by the application of modefied Goodman stress diagram. The coresspounding com-puter program is worked out in FORTRAN and the calculating results are obtained of 35Mnp and 40 CrMo steel sucker rods under different parameter coordinates. A rod string de-sign criterion is perfected by the analysis of these results in deep well production with pump-ing units.

Key words: Deep well pumping technique, Rod string design, Criterion