The invention provides a log system and an application method thereof; the log system includes a server and a plurality of service process terminals, the server includes a log storage unit and a log server unit, the service process terminals include a log client unit, a service process unit and a log interface unit. The method includes that a connection relation of the log storage unit and the plurality of service process terminals is established; ID numbers are allocated to each service process; log rule information is written to service process terminals; the information with service process terminal ID and the log information containing log category and log rank are sent to the log client unit by the service process unit; the log rule information is acquired by the log client unit according to the service process terminal ID from the log storage unit, and the output form of the log information is determined according to the log category, the log rank and the log rule information. The invention enables users to define the log category, the log rank and the output form of the log information flexibly and ensures users to view log information conveniently.