In the era of big data, personal information has been widely shared and used, which facilitates personal life, social production and public management but also brings the risk of personal information abuse.Personal information has multiple values involving with personality dignity and freedom, economic use, and public management. Meanwhile, the stakeholders relevant to personal information have become more and more diverse, leading to increasingly urgent demand for sharing and using personal information. With the great improvements in the processing efficiency and transmission rate of personal information, it has become much easier to share personal information, which makes the application of the principle of informed consent more difficult. In this circumstance, "Rational Expectation"rule becomes a new option of personal information protection in the era of big data. By assessing the risk of personal information sharing with matrix method in application contexts, it discusses the criteria of risk control under rational expectation rule. If the risk assessed is at the level of low risk, the sharing and use of personal information in this context complies with the rational expectation rule; If the risk assessed is at the level of medium risk, it is necessary to take measures timely and actively to reduce the risk and reassess the risk; If the risk assessed is at the level of high risk, the rational expectation rule is not applicable, the personal information controller should significantly inform the information subject and obtain consent before sharing the personal information. If there are multiple risk points in the application context, when and only when each risk level judged must be low risk, the rational expectation rule can be applied. Based on the rational expectation rule, we can achieve the balance of interests among personal information protection, digital economic development and public interest maintenance, so as to coordinate the promotion of digital innovation, economic development and social progress, and realize the unity of effective protection and rational use of personal information.