Abstract: Fault injection（FI） is a powerful method for the testing and evaluation of fault tolerance mechanisms（FTMs）, which may widely be used during all phases of the development of fault tolerant computer systems. The technique of FI cannot be applied correctly and widely unless it is based on a consistent understanding of FI philosophy. FTM is the application object of FI and its characteristics as seen in testing and evaluation processes are discussed in detail. And then an FI model is described as a 6 tuple. The attributes of each factor are deeply analyzed. As the actual application process of the FI model, an FI independent experiment algorithm（FI IEA） is presented at the same time, and some key problems on how to implement the algorithm are discussed.