The invention discloses a system visualization subpackaging method used for improving the debugging safety of a conventional island of a nuclear power station. The method comprises the following steps that a debugging task of the conventional island of the nuclear power station is set up and split to form debugging task subpackages, and the boundaries of the debugging task subpackages are labeled on a drawing to form the drawing; a device list is listed according to the drawing; a debugging whole network graph is formed according to the device list, devices, debugging logic of parts and time sequences included by the debugging task subpackages are determined according to the debugging whole network graph, and then classifying and filing of debugging technical documents are finished. The method has the following advantages that the subpackages are reasonably divided; main debugging activity content of all the subpackages, logic relations among the subpackages, and the time sequences are determined; time for debugging beginning and ending of all the subpackages is clear and definite.