Software migration is an inherently knowledge intensive activity, which requires a great amount of expertise and experience from different sources. Knowledge-based approach to software migration has a great potential for improving traditional approaches. In this paper, an Ontology-based PlaTform-specIfic software Migration Approach (OPTIMA) is proposed. Firstly, the background and the related work are introduced, and the ontology design for platformspecific software migration is discussed. Secondly, the architecture and workflow of OPTIMA are illustrated with a prototype tool. Thirdly, the case study is used for experiments with the approach and the prototype tool, and finally, the conclusion is drawn and further research directions are speculated.