A data inspection system includes: a communication circuit arranged to operably communicate data with a plurality of attributes filtering devices to receive multiple activity records which are generated by the plurality of attributes filtering devices and corresponding to multiple IoT devices in a plurality of target IoT systems; a storage circuit arranged to operably store the multiple activity records received by the communication circuit; and a data classification circuit coupled with the storage circuit and arranged to operably classify each of the multiple activity records received by the communication circuit based on N attributes to form M data groups; wherein N is 2 or an integer greater than 2, while M is at least two times of N.