Grasping the risk issues correctly is the key to ensure the scientificity of trust decision-making. Aiming at the insufficient understanding and research of the nature relationship between trust and risk in the present research on dynamic trust relationships, this paper proposes the theoretical model and the decision-making model of trust relationship from the perspective of risk, analyzes in detail and gives out the nature relationships between trust and risk, trust decision-making and risk decision-making. Trust is deemed to another expression of risk. Trust decision-making is risk decision-making. The scientificity of security decision-making is enhanced and the security decision-making becomes more rational, more comprehensive and more objective by the analysis of security decision-making process of trust, risk and credible decision-making.