Heating ventilation and air conditioners（HVAC） in commercial buildings have become important demand side resources providing power system ancillary services. A novel interactive control strategy to coordinate HVACs with power grid is proposed from the perspective of building aggregators. Firstly, a physical modeling and prediction method for the interaction capability of commercial buildings is proposed. Then the interaction capability curve（ICC）of a commercial building is established based on the global temperature adjustment strategy. After that, the aggregation and decomposition algorithms are proposed, based on ICCs of buildings and the idea of bidding and clearing. Simulation results show that the proposed method can be adapted to a variety of commercial buildings. An aggregator can predicate and visualize interaction capabilities of buildings, coordinate buildings to track the control target precisely, and distribute the burden of reduced service level much evenly between all temperature zones.