1. A power system data model conversion method of a power system data model conversion system including a database which stores data related to devices of a power system including at least one of a transformer, generator, and a power line, and stores information of a connection relationship between the respective devices; and a server connected to the database that performs analysis of the power system, the method comprising: an instance readout step of reading out all instances from the database, which correspond to the devices, respectively; a connected relation analysis step of following a connection relationship of a main device, which is among the devices and is subject to power system analysis, with the other devices which are connected to the main device; a property information aggregation step of aggregating property information recorded in one or more of the instances into a single instance and also erasing the instance unnecessary for the power system analysis on the basis of the connection relationship in the connected relation analysis step to create a power system analysis data model; and a power system analysis step of performing analysis of the power system using the created power system analysis data model.