Abstract: Taking G grade oil well cement as the study target, the evaluation method for oil well cement endurance was studied, to supply an theoretical foundation for evaluating cement mechanical performance. The long term strength and breaking ability of cement were tested by triaxial mechanical test instrument. Considering the theoretical analysis, the long term strength and breaking ability were determined as the two key factors for cement endurance. The study tested indoor only the cement itself, but not the cement with any additive. The next step for the study should focus on improving the cement endurance by adding some additive.