This paper develops an online control strategy for the multiple chillers with constant flow of cooling water and chilled water (primary side). The strategy is based on the performance map which indicates the chillers' near optimal control to save their energy consumption. The map is formed with diversified data sources and updated periodically to ensure its good quality. Two simulation studies are conducted to validate the effectiveness of the proposed strategy in saving the chillers' energy consumption. In Study 1, the proposed strategy is simulated during 8 weeks in August and September, with its map updating and not updating respectively. The result shows that periodically updating the map can make the proposed strategy more effective in energy saving. And the computation time per execution of the proposed strategy is feasible for online application. In Study 2, the proposed strategy is simulated from May to November. The result indicates that the proposed strategy is insensible to the initial history data, and can reduce the chillers' energy consumption comparing with the sequence strategies.