International investment law protects legitimate and genuine investments and does not include investments that violate host states’laws or are in bad faith. This requires investors to carefully evaluate investment risks and rationally plan investment behaviors in the stages of investment access, management and dispute settlement. When a host state proposes that an investor has violated the law, arbitral tribunal usually excludes the jurisdiction of case based on the legality requirement in the investment definition etc., but this does not mean that any illegal behavior should be terminated at the jurisdiction stage, which still needs to be examined in combination with factors such as point-in-time and severity. Therefore, the treaty regulation of investors’behavior should focus on clarifying the scope of investors’obligations, introducing independent illegal-defense rules and establishing behavior supervision mechanism, so as to construct a symmetrical structure of rights and obligations system.