Abstract: Fitness-for-Service(API 579-1/ASME FFS-1-2007) is considered to be the international mainstream residual strength assessment standard for oil and gas pipelines. However, there are still many technical difficulties in the practical application of this standard. For this reason, the concept "pitting area occupation ratio" was introduced for pipeline, and the non-discrete characterization model related to the residual strength coefficient and the residual wall thickness ratio was put forward to successfully realize the continuity of discrete 8-grade pitting standard modes. The image processing platform built by MATLAB was used to complete the safety assessment and residual life prediction of pipelines in any state between the standard modes of 8-grade pitting corrosion. After the perfection of assessment rules in API 579-1/ASME FFS-1-2007, the engineering practicability was improved, and the difficulties in pipeline safety assessment and dynamic prediction of residual life were overcome, so it is believed to be of important technical and economic value.