The linear superposition principle applies where the governing equations of a physical problem are linear. Keeping other factors unchanged, in a ventilation system, the change of the air flow has a non-linear relation with that of the air resistance, and thus the linear superposition principle does not apply directly. Based on the Taylor's expansion, however, the superposition feature can apply to some extent for the changes of the air flow and the air resistance in a ventilation system by the linearization of the non linear equations, which means that in a ventilation system the variations of the air resistance of different parts can approximately be added up to calculate the air flow variation when the changes of air resistances are relatively small. The error of such kind of superposition increases with the expanded range of air resistance's variations. The superposition feature of a ventilation system is important for the evaluation and identification of the air flow's fluctuations. For a large and complex ventilation network, however, the application of the superposition method requires further studies.