The deflection control of the tube used for the New 2.3m Australian Technologies Telescope is introduced. It is the purpose to keep the relative correct position between primary and second- ary mirrors when the optical axis is pointed to any object. All the deflection calculations for the component parts of tube-center ring

primary truss

secondary truss

top-end ring

and strusts are given by the classical mechanics of materials when the optical axis points to the two positions of zenith and horizon. Then the optimum configuration of the primary truss is given to simultaneously annul both the axial and lateral deflection of the primary mirror with respect to the secondary mirror.