Abstract: The crack propagation life was calculated under the tensile load using the sectional type numerical integration method based on the Paris formula considering the relation of geometric modified index f and crack size a. The Monte Carlo method was also used to get the reliability of different types of surface crack propagation lives. The results showed that taking the defect as an elliptical crack governed by depth ration and aspect ratio is better than circular arc crack or straight-edged crack only governed by depth ration. The sucker rods with the circular crack break first. The critical crack propagation life based on the traditional fracture mechanics is not accurate, and the sucker rod may break before the critical crack propagation lives.