In view of laser systems, a new laser beam expanding system is researched, which adopts an off-axis reflection optical system. For beam expanding equipments requiring high precision and stability, the accuracy of the system is ensured to less than 0.02 mm through material selection, opto-mechanical structure design, rigid design and simulation analysis calculation. For multi-axis debugging being required by beam expanding equipments, a multi-degree of freedom adjusting mechanism is designed to realize three axis rotation and translation. The results show that the design of system structure is rational and meet the requirements of the beam expanding system.