Abstract:  For effective control of risk, risk analysis of medical device employment is addressed by using failure mode effects and criticality analysis (FMECA) in this paper. After the properties of medical device employment is analyzed, based on fuzzy mathematics and grey relational theory, an improved FMECA method for the problem is presented. Compared with the existing FMECA methods, the proposed method has the advantage of having the ability to deal with uncertainty. As an example, the proposed method is used to analyze the operation of a C arm X ray machine. Result shows that it can obtain the risk priority of the failure modes and select its most safe operation policy.