Abstract: Aimed to the charactoristics of toplogical complexity of ventilation system, the ventilation subnet-judgment rules，all subnet recognition，the simplification and application to the topology of the simplest quasi-equivalent ventilation by researching the topology character and the simplifying-process and principle of complex ventilation network had been researched，what's more，all of this enriched the topology theory of complex ventilation network.

Key words: Complicated ventilation network, Subnet recognition, Simplification, Simplest quasi equivalent topological