Objective To explore the key factors which affect maintenance cost of large-scale medical equipment. Methods The basic factors which affect maintenance cost of medical imagining equipment were summarized. The relationships of them are analyzed and then an interpretative structure mode of each factor was set. Additionally, the multiple relationship and controllability between each factor were also analyzed and the judging standard of key factors was set. Results The maintenance policy and mode were the key factors which affect maintenance cost of medical imagining equipment. Conclusion High quality maintenance for equipment condition and scientific optimization of the maintenance policy are necessary to fundamentally reduce the maintenance cost of large-scale medical equipment.