Abstract: In response to the security issues of space-based information systems in electromagnetic and network aspects, a security threat conceptual model including wireless electromagnetic intrusion and wired interconnection intrusion is proposed, and typical types of security threats are given. Firstly, based on the analysis of space-based, link-based and ground-based threat objects, the security threat chain including situation awareness, strategy generation, electromagnetic/network access, target attack and effect evaluation is discussed. Secondly, the main threat behaviors are studied, and a hypothetical security incident case that led to the loss of control of the satellite's attitude is presented, illustrating the serious consequences that security risks might cause. Finally, in response to the demand for reducing and preventing security risks of space-based information systems, some suggestions for deep security reinforcement are put forward.