Abstract: In the view of information ecology theory, this paper studied the optimal allocation of library collection resource to provide a new perspective for the knowledge and information service and promotes the healthy and orderly development of library. It analyzed the current situation of information ecology imbalance including the lack of information subject and the uneven distribution of resource in the digital library. Duet to the similarity of information ecology and digital library in the components, functional objectives and application value, it expounded the feasible measures for library to introduce information ecology theory to optimize the allocation of resources from the orientation of service, social demand and purchasing decision-making.