In a method and system for calculating CRC, a Partial CRC is first calculated directly according to a segment of a message. Then, a First Code including the Partial CRC appended with a plurality of zero-bytes is generated. Finally, the Adjusted CRC is calculated according to the First Code. Therefore, an Adjusted CRC can be derived directly from each segment of a message. After all segments of a message are received, all the derived Adjusted CRCs are merged to obtain a Final CRC of the message. The method and system can be quickly prototyped and implemented to various systems due to its simplicity.