Variable air volume (VAV) air conditioning control system has the feature of multi-control loops. While all the control loops are working together, they interfere and influence each other. This paper designs the decoupling unit in VAV air conditioning system in the method of diagonal matrix decoupling. Lonworks technology is adopted in VAV air conditioning decoupling control system so that data could be exchanged among multi-loops. It is suitable that decoupling compensation coefficients among multi-loops are handled as network variables of Lonworks technology. Experimental results demonstrate that the combination of the diagonal matrix decoupling and Lonworks technology can improve the performance of the VAV air conditioning control system. (C) 2005 Elsevier B.V. All rights reserved.