For researching the construction caverns of underground powerhouse， on the basis of the analyses of main affecting factors in construction ventilation and the study of air volume and air pressure calculating theory， and according to the actual construction and application，the calculating method of air volume and air pressure could be determined. Using the determined calculating method，according to simulation principle of cavern of underground powerhouse ventilation， the emulation calculation system of construction ventilation is established. From the emulation calculation system， the controlling factors of air volume and air pressure could be calculated. With the data， the ventilation equipment is chosen，the ventilation project arranged and a corresponding optimization suggestion presented. This paper could offer beneficial reference to similar engineering.