Abstract: A result of safety evaluation was educed according to the rules of credible recognition after a index system in colliery ventilation safety evaluation was established. An unascertained measure model was constructed and the unascertained measure values of all evaluation indexes were calculated. This method can solve a lot of unascertained problems in ventilation system evaluation, and also can analyze the ventilation system quantitatively. Exemplification indicates that the evaluation result is consistent with actual instance if the method of unascertained measure evaluation is applied in colliery ventilation safety evaluation.