Free-form deformation is an important geometric shape modification method in computer animation and geometric modeling. The authors explore it by means of functional composition via shifting operators in this paper. When the object to be deformed is represented by triangular meshes and the deformation tool is a B-spline volume, the deformed object can be accurately described as a set of triangular Bzier patches, whose degree is the sum of three directional degrees of the B-spline volume. The proposed method also solves the sample problem of free-form deformation, because free-form deformation acts on triangular meshes rather than points.