The invention provides an inspection method of a grade protection security boundary. The inspection method comprises steps of firstly installing probe software for machines connected to the network in a domain, wherein probes in different domains communicate with each other once at an interval of 24 hours, and returning data of a source IP address, a target IP address and a feedback result about whether the communication is successful or not; uploading the returned data to a database server in an unified manner; marking according two pointing directions between every two domains based on domains to which the source IP address and the target IP address belong; according the quantity M of the domains, establishing M*(M-1) sheets to store the returned data; using repeated data fed back by probes in the same domain to carry out summarizing so as to obtain a boundary access strategy between domains; and finally, comparing a processing result of the returned data every time with the processing result of the previous time to obtain an adjustment change condition of a security boundary. According to the invention, identification efficiency and accuracy can be improved; under the condition that the security boundary is often changed, the validity of the security protection boundary is ensured and hidden safety hazards can be timely found.