Although the concept of Knowledge Worker was brought forward half a century ago, a clear picture about the profound connotations has been not given yet.  The definitions of knowledge worker were reviewed from four prospects, namely work content, manner, nature and individual character. Frequency statistic analysis indicates that the eight characteristics, including autonomous, well educated etc are highly recognized by researchers. Thus, classify knowledge workers was classified into three sorts of criterions according to their strategic character, knowledge work nature and career type.  New definition of knowledge worker is given.  Its character and classification were also appraised briefly.