Abstract: This paper studies the entire expression of three dimensional finite element method volume data field. The importance of setting up the entire expression of data field is discussed, and B spline hyperpatch in large dimensions is adopted to represent the geometry shape and data distribution. Without transforming the entire feature, the neighbor elements are merged to reduce the scale of the data field in order to represent the data field by simple expressions. Furthermore, the iso surface extraction algorithm of FEM data field based on B spline hyperpatch is also provided.