Australia can't afford to be naive when it comes to selling its critical infrastructure to an increasingly assertive China, the head of a defence think tank warns.

Australian Strategic Policy Institute executive director Peter Jennings has warned Treasurer Scott Morrison Chinese investment can no longer be welcomed as business as usual, as China continues to flex its military muscles in the disputed South China Sea.

"China is changing how it behaves internationally and how it deals with countries such as Australia - we can't afford to be naive about this," he writes in The Australian on Saturday.