With the improvement of the digitization degree of the aircraft, a large amount of multi-source and heterogeneous data will be generated throughout the full lifecycle of an aircraft, which plays a crucial role in ensuring its safety. This article reviews common types of data sources within the aircraft"s lifecycle, including initial airworthiness design data, operational reliability data, operational maintenance data, and onboard equipment data. By combining the data characteristics of different data source types, the article introduces measures for the fusion application of multi-source heterogeneous data and provides a detailed analysis of the four stages that data fusion technology has undergone. On this basis, the fault diagnosis method of fusion data is introduced. Compared with the fault diagnosis analysis of traditional single data source, it is concluded that the fusion application of multi-source heterogeneous data can analyze the fault causes more accurately, and play a role in assisting troubleshooting and maintainability design, which is the development trend of data application technology in aircraft fault diagnosis.