Abstract To make the VAV system controlling highly efficient，energy-saving and comfortable，the authors study the ratio-control of fresh-air and indoor-air，the temperature-control and humidity-control，the frequency-control of fans in the four-pipe-system．From the point of view of intelligent building controlling we analyse the conversion condition of all kinds of work-point by using enthalpy-humidity chart，adjusting the wind-system or the water-system to meet the demand of air-condition design．Some suggestions for the control of transition seasons are presented in the end．
