A decoder and an operation method thereof are provided. The decoder includes a pre-unit, a database, a data filter, and a scheduler. The pre-unit provides packet information of a data stream. The database records a plurality of parameter sets. The scheduler fetches the corresponding parameter sets from the database according to the packet information, and saves the parameter sets into the data filter. The data filter compares the data stream with the saved parameter sets and outputs a comparing result. Therefore, the present invention reduces the cost of the decoder.