Abstract: Telecom fraud seriously destroys social trust, but the psychological mechanism of people being easily deceived and how to effectively prevent telecom fraud at the individual level are still lacking. From the perspective of telecom fraud victims, this paper analyzed "who", "why" and "when" choose trust. "Who" is more vulnerable to telecom fraud? We analyzed the victim's susceptibility to telecom fraud, the key factors including demographic characteristics, personality characteristics and cognitive characteristics. "Why" the victims choose trust, which is influenced by fraud stories and social influence techniques. And "when" the victims to choose trust, which is related to the psychological dynamic factors induced by the interaction between the victims and fraud information. Three models were used to explain the internal mechanism, which are Elaboration Likelihood Model, The Scammers Persuasive Techniques Mode and A Working Model of Susceptibility to Online Influence. But these models can not cover all types of telecom fraud. Future research can be carried out in the integration and development of the model, the enrichment and improvement of the research on the types and stages of telecom fraud, the improvement and innovation of causal research methods, and the practicality and operability of intervention research.