Abstract: Migrating the Cobol code to a new platform such as Java is an effective method to alleviate the burden of maintenance of the Cobol code. How to migrate Cobol data to the new platform is one of the basic problems to be solved. Most research work directly casts Cobol data to primitive data type such as int or float in modern programming language. However, this simple data mapping method doesn't keep the Cobol semantic and thus makes the translated code run inconsistently with the original Cobol code. In this paper, a pure Java encapsulating method is presented using the data modeling technology to map the Cobol data to Java type system with functional equivalence. Based on this method, a Cobol2Java translator is implemented. The translator is also applied to a real business system of about 4 million lines of Cobol code. Test results show that this tool could translate the Cobol system to Java successfully and without any human interaction.