The basic concept, main advantage, architecture, method and application of multi－sensor data fusion are described. Data fusion is the process of combining, correlating, and associating data from multi－sensor or other information sources to identity estimation and assessment of situations. Some general problems on fault diagnosis are introduced. The process of data fusion of fault diagnosis are also introduced. Their specialty and the layered fusion architecture fitting with fault diagnosis of control system are analyzed, and an architecture of fault diagnosis which is based on the information fusion are deeply investigated.