Abstract: As one level of the United States'proof standard system,probable cause is a specific standard with a special and important standing.The judges make decisions based on a certain quantity of information about cases.And the judging criterion is one from an ordinary person.Probable cause is often used in the processes relating to investigation,such as search,seizure and arrest procedures.It has great influence on criminal procedure mainly in two aspects.On one hand,it prevents state power interfering and intruding citizens'freedom and privacy arbitrarily.On the other hand,it is not required beyond reasonable doubt in investigation.It provides the criminal justice administration a relative looser standard to fulfill their duties.So that it balances the exercise of state power and the protection of citizens'private rights.Reviewing criminal justice in the United States,the probable cause standard may provide reference to Chinese criminal evidence law.