Estimating maintenance cost is an important part of LCC (life cycle cost) management. Due to the limitation of maintenance cost data of SAM system, GM (1,1) model is briefly analysed, the precision of maintenance cost data is also discussed. Then, aiming at a new type of SAM system, the application of GM (1,1) model is systematically discussed, and the precisions of former information GM (1, 1), new information GM (1, 1) and metabolism GM (1, 1) model are compared and analysed. According to the result of the analysis, metabolism GM (1, 1) model is accurate and less sophisticated.