Abstract: The unified system of principal offender can overcome the problem that principal offender and accomplice are difficult to distinguish. At the same time, it has the advantages of more scientific and reasonable conviction and punishment, which has gradually been supported by some scholars. However, with the introduction of objective imputation theory, the unified system of principal offenders is further analyzed. Because of the lack of imputation judgment, it cannot implement the principle of legal interest and imputation in the theory of crime, and then it will face the risk of collapse in an all-round way. Therefore, it is indispensable for a reasonable accomplice system to use objective imputation theory to judge the liability. Its importance lies in the fact that the imputation judgment can solve the problems of behavior imputation and result imputation in joint crime.