Abstract: Prediction of fatigue crack life of sucker rod with variable amplityde loading has been studied in the lighe of stochastic fatigue principle. Based on investigations from sucker rod manufacturer and oil field operator, sucker rod signals from 19 wells with good representation were gathered and the load spectra wave established. Nominal stress method, local stress-strain method and fracture mechamics techniques are used to predict the fatigue crack life in theoretical anlysis. Simulation tests with programmed loading were performed. Statistical data, theoretical prediction simulation tests have given consistemt life prediction with 99.9% probability of survival, from which the "Mark Life" of grade C sucker rod is thus given. Propesals for further research are also made in the paper.