It is very important to evaluate the discovered rules in KDD (knowledge discovery in database). An evaluation method for causal rules is provided in this paper. The new and valid knowledge expression (language field and language value) and the reasoning mechanism (qualitative induction mechanism of causal relation) are used. The method is general and interactive. Its construction and the algorithm are given, and its validity is proved through case. By the comparison with the related work, it is proved to be an advanced method.