Abstract: Abstract: On the diversity and heterogeneity of crop model system, the integration method based on Web service was studied. By analyzing the architecture of crop model system and interactive features between function module, service partitioning based on service-oriented architecture (SOA) was studied. Combining with Web service identification and segmentation principle, the partition and the service combination structure of crop model based on Web service was proposed. Then the model system was divided three Web service including Web service of model calculation, Web service of weather data and Web service of soil data. The service package using "contract first" Web services development technology was designed. The modeling process based on web services contract-first (WSCF) was described in details and the automatic generation of Web services description language (WSDL) Deed and services code framework was achieved by use of related tools. The knowledge model system for wheat management as an instance was reused through four steps based on Web services, and the concrete package steps were service data modeling based on crop model metadata, service information modeling, service operation and the interface modeling, and service implementation using C# language under VS2008 ASP.Net platform. Taking the reused knowledge model system for wheat management based on Web service as the testing target, the effectiveness was verified in a real network environment. The output solution of the system was consistent with the result of the original knowledge model system for wheat management using weather data and soil data of 75 cities at prefectural level of Jiangsu province in year 2010. It showed that the crop models system integration method adopts unified model service contract, making full use of the cross platform and cross programming language advantage, which promoted the efficiency of the model system integration, which solves the problem of interoperability between heterogeneous systems. The crop model system of Web service encapsulation, making full use of the crop model resource of software components, the development of relevant documents and other resources, which improved the reuse level of crop model resource. Analysis from the point of view of model of business functions, reassignment and development services were independent, and the designment of the service through the WSDL addressed specific requirements, which shielded the underlying technical details and related agricultural domain specialized knowledge and improved the application of crop model. These results provide a methodological guideline for crop model system integration.