"对国家安全的危害" can be translated into English as "the harm to national security" or "the threat to national security" (depending on the context, with "threat" often implying a more imminent or direct danger, while "harm" can refer to broader negative impacts).
For example:
"This behavior poses a serious harm/threat to national security."
(这种行为对国家安全造成了严重危害/威胁。)