The Supervision Law of the People’s Republic of China, first revised in 2024, has undergone a tiered reconstruction of the system of compulsory supervisory measures, yet it fails to address the fact that supervisory authority is incomplete. Existing research on the nature of supervisory assistance is divided into theories of administrative assistance, criminal judicial assistance, and a compromise view, all of which have their shortcomings. Based on whether supervisory organs possess statutory enforcement powers, assistance measures provided by public security organs to supervisory authorities are categorized into “cooperative assistance” and “enforcement assistance”: the former manifests as “supervisory decision-making-supervisory enforcement-public security cooperation,” while the latter is characterized by “supervisory decision-making-public security enforcement.” This classification is supported by the theories of government linkage, division of labor in decision-making-enforcement-oversight, and dichotomy of police power functions. It clarifies the nature of different supervisory assistance behaviors and establishes a logical starting point for subsequent procedural construction. Based on this, in the design of procedural mechanisms, differentiated procedural rules are constructed around the four stages of submission, review, enforcement, and responsibility for cooperative and enforcement assistance, ensuring that supervisory investigation powers operate in accordance with the law while providing clear guidance for public security organs’assistance in supervisory activities.