Abstract: The fracture of the corrugated pipe has a dad effect to the operation of reactor which can cause the small-break LOCA. The corrosion is the key reason of the fracture. On the base of the analysis on corruption reason of the sylphon bellows and combine the characteristic of the limited sample point of it, the Grey theory was used in the assessment of corrosion life span of corrugated pipe in nuclear steam system. Through applying the GM (1,1) model in inferring the discipline of corrosion quantity and combining traditional statistical method, the corrosion life of steam pipe was evaluated. It indicates that the model is precise, simple and the result is reliable.