Enterprise diagnosis is a complex process in which various enterprise knowledge are involved. It is proved that hybrid inference mechanism is an effective solution to deal with such problems. Aimed at the issue that current representation of diagnosis knowledge depends excessively on the inference mechanism, the strategy that separates the enterprise model knowledge and the inference knowledge is adopted in this paper. By systematically analyzing the diagnosis knowledge of enterprise model, a general representation of diagnosis model knowledge is put forward based upon XML schema and its validity and feasibility is tested through a practical application.