Abstract: Axial support system plays an important role in axial position and deformation of primary mirror. In order to profoundly develop such study, axial hydraulic Whiffle-tree support was introduced in the foundation of structure Whiffle-tree. First, according to the principle of kinematic constraint and support based on three axial points, the characteristic and category of Whiffle-tree system were introduced. Especially, the difference between structure Whiffle-tree and hydraulic Whiffle-tree was compared in detail. Then the model building method was elaborated, and an axial hydraulic Whiffle-tree support system for a large aperture primary mirror was selected to be calculated and optimized in statics. As a result, the mirror deformation is 18.6 nm which satisfies the design requirement and the rationality and accuracy of such modeling method are also certificated according to comparison between two different modeling methods.