A semantic-based information integration scheme for MedImGrid (medical image grid) is presented, which creates parent-ontology (HL7-RIM ontology) based on HL7-RIM (health level 7 referenced information model), and adopts hybrid means to construct the hierarchical structure of MedImGrid global and local ontologies. The HL7 (health level 7) gird middleware is developed based on Agent and middleware technology, which gives the semantic parsing capability to HL7 intelligent Agent to support grid service encapsulation and uniform access of heterogeneous data sources. The interrelations of data modes at ontology layer are denoted with ontology tag and used to support the semantic parsing and mapping between different medical data sources referring to MedImGrid ontologies. MedImGrid prototype is based on CGSP2 (China grid support platform v2.0) and adopts global and local semantic mapping loosely coupled means, and its special layered structure makes resource sharing and matching across systems and hospitals more efficient.