Much attention has been pay at simulation model maintenance and reuse in Modeling and Simulation (M&S) community. Model reuse can save time and expense of simulation system development and improve the quality of simulation software. However, model reuse is still an open challenge. Discrete EVent Specification (DEVS) is applied to describe simulation model by many researches. A DEVS Ontology (DEVSO) is presented to describe the simulation models and record their changes. Model Modification Operations (MMO) are defined to describe the model changes, which are based on Ontology Atomic Operations (OAO).An approach based on similarity evaluation for model reuse is also brought forward. The approach can evaluate the reusability of models by calculating their similarity degree. The adaptation rules can also be reasoned by the approach, which is the sequence of MMOs to modify model to meet the requirements.