The utility model provides a precipice cavity ventilation system, the cavity formation is between the facade and precipice of dell building, the facade with both sides have the connection of two lateral walls between the precipice, wherein, ventilation system includes: the top ventilates and constructs, locates the cavity top, the top ventilates to constructing and is formed with the top vent, theinside and the outside of cavity are passed through top vent intercommunication, the bottom ventilates and constructs, locates the cavity bottom, the bottom ventilate construct in be formed with thebottom vent on two lateral walls respectively, blower device corresponds the top vent set firmly in the cavity top. Borrow this, set up the vent at the bottom both sides and the top of cavity to utilize the hot pressing effect to form natural convection and ventilate, and set up the forced draught blower in cavity top vent department, in order when forming the hot pressing effect, to carry out mechanical convection and ventilation through opening the forced draught blower unable, improve in the cavity air quality and safeguard that the building is used and inside personnel are healthy.