Due to the difficulty of finding recirculation of airflows in a complicated ventilation system, a searching strategy is proposed based on depth-first search method for searching recirculation in complicated ventilation networks. The depth first method is introduced briefly while the searching strategy for tracing recirculation in a network is introduced in detail. The proposed method is then used in a copper mine for searching the recirculation of airflows. The mine ventilation system is solved by VENTSIM software first for getting all the airflows information, i.e. the nodes and directions. Then the data of ventilation system is stored in the matrix for tracing the recirculation in the network. A few of recirculation of airflows are found and are compared with the VENTSIM solving results. It is found that the searched results agree with the VENTSIM solving results of the ventilation system. It is concluded that the proposed method has the capabilities of tracing airflow for finding recirculation.