Abstract: Based on the analysis of the major satellite in-orbit faults during the past 10 years, six types of catastrophic and serious faults are identified, along with the principal fault modes of typical onboard equipment/components. On this basis, the main causes of the in-orbit faults are analyzed, and it is shown that the following factors are important: the sufficient ground validation of new technologies and new states, the stability of the complex processing, the quality of components and electric assembly, the knowledge of the space environmental influences, the software design, and the proper ground operation. Suggestions are given correspondingly on the countermeasures, to provide a reference for the identification of the weak links of key equipment/components and the related reliability design both in the unit and system levels.