The invention discloses a building environment monitoring method based on a circulating system. The building environment monitoring method comprises the following steps: through a plurality of air detecting devices dispersed inside a building, sampling air quality of each area inside the building, and sending obtained sampling data and position data of the air detecting devices to central controlequipment; processing the sampling data and the position data sent by each air detecting device by the central control equipment, starting a corresponding air purifying device, and monitoring the restservice life of the air purifying device; and when the rest service life of the corresponding air purifying device is lower than a preset threshold value, cleaning the air purifying device by clean water sequentially treated by a rainwater collecting device and a rainwater purifying device. The invention further discloses a building air monitoring system based on internal cycle. The building environment monitoring method and system have the beneficial effects that: a local air quality condition in the building is monitored, indoor air quality can be improved in a targeted mode, and influenceson a surrounding environment are reduced.