Knowledge worker is a key factor in the innovation and enterprise competence. The evaluation of their value, which is a basis of many human resource management functions, is very important for the enterprise to manage the knowledge worker effectively. But the knowledge worker value is dynamic, connotative and multidimensional, which makes it difficult to evaluate accurately. Rough set theory, which is widely used in classification, appraisal and mode identification, has many advantages, such as no information loss, flexible, extendable, is involved in this paper. The evaluation approach is also expatiated. To test the reliability of evaluation, a case is used, which improve that rough set theory can be used in evaluation of knowledge worker value.