The vision of Internet of Things (IOT) promises a prosperous future for grain storage quality control by integrating all sensors deployed in the individual grain bins into a global grain storage system. However, since the data format and the data semantic of the monitoring systems are not unified, heterogeneous systems equipped with sensor networks are pending integration and have difficulty in semantic interoperation. In this paper, we design a semantic middleware to promote the data interoperability of different grain storage systems. The proposed semantic middleware uses a multi-layer architecture and provides four basic services: semantic mapping service, query service, publish service and ontology management service. Raw sensor data are converted to RDF format by semantic annotation. Semantic data are stored in the knowledge base and can be queried and reasoned. The semantic interoperation middleware will promote data interoperability, information search and retrieval, automatic inference and extendibility in the global grain storage internet.