Digital libraries are complex systems and this brings difficulties for their evaluation. This paper proposes a hierarchical model to solve this problem, and puts the entangled matters into a clear- layered structure. Firstly, digital libraries (DLs thereafter) are classified into 5 groups in ascending gradations, i.e. mini DLs, small DLs, medium DLs, large DLs, and huge DLs by their scope of operation. Then, according to the characteristics of DLs at different operational scope and level of sophistication, they are further grouped into unitary DLs, union DLs and hybrid DLs accordingly. Based on this simulated structure, we introduced a hierarchical model for digital library evaluation, which evaluates DLs differentia tingly within a hierarchical scheme by using varying criteria based on their specific level of operational complexity such as at the micro-level, medium-level, and/or at the macro-level.. Based on our careful examination and analysis of the current literature about DL evaluation system, we conducted an experiment by using our own DL evaluation system along with its criteria for unitary DLs at micro-level. The main contents resulting from this evaluation experimentation and also those evaluation indicators and relevant issues of major concerns for DLs at medium-level and macro-level are also to be presented at some length.