In this paper,we mainly focus on the hypernormal form for a class of fourdimensional nilpotent vector fields,and the results are applied to simplify the practical engineering models in the highdimensional nonlinear dynamics. We improve and develop the further reduction theory of the normal form proposed by Sanders,Baider and KOW,and based on the method of linear grading function,multiple Lie bracket and the new notations for block matrices,we obtain the three order and the five order hypernormal form,respectively,and then the results are applied to simplify the circular truss antenna models. The introduction of the new notations for block matrices gives a new method for dealing with the calculation of big size block matrices,which brings conveniences for the later research.