<p>Low earth orbit (LEO) satellites have the potential for global low-latency connectivity and provide high-speed Internet services to users around the world. However, LEO satellite networks (LSNs) data is open, and attackers can easily obtain information such as network topology and satellite orbit space position, and then perform a link flooding attacks (LFAs) on the inter-satellite links (ISLs) to block the bottleneck link and cause network failure. This paper provides a detailed analysis of the failure mechanism of the LSN considering the gateway under LFAs, the failure simulation algorithm is developed and the LSN failure state transition is defined and described in a formal way. Under different route and attack schemes, the survivability of the network is evaluated using evidential reasoning (ER) rule combined with the utility function. We find that ISL load imbalance is an important reason for LSNs vulnerability. Meanwhile, a resilience enhancement scheme for ground segment gateway layout optimization of LSNs is proposed, and a whale optimization algorithm with integer coding is developed to solve the layout. A simulation of an instance constellation indicates that the optimized gateway layout improves the average survivability of the LSN by 6.4% and the average communication connectivity by 15.4% compared with the random gateway layout. The performance of the network in terms of latency, packet loss ratio and throughput are also significantly improved.</p>