With the continuous development of space-based networks, Software Defined Networking (SDN), relying on its decoupled architecture of control plane and data plane, has become an important method for space networking. However, while the centralized scheduling characteristic of satellite-borne controllers strengthens space-ground collaboration capabilities, traditional ground-based security testing methods face the risk of failure when confronted with the high latency and dynamic topology characteristics of space-based networks. Therefore, this study designed a multi-agent security testing framework. It proposed three algorithms: a topology construction algorithm, a routing prediction algorithm, and an attack propagation analysis algorithm. It designed a triplet model for four types of flow risks, covering 14 types of space-based network risks, achieving risk quantification. This study provides a security testing framework for space-based networks, facilitating the evolution of software-defined space-based networks towards high resilience.