A common reference calibration method was proposed for the precision alignment of off-axis two-mirror optical systems with adjustable focus, which ensured that the guide rail and the optical axis of the primary and secondary mirrors were precisely aligned with the same reference, and realized the parallel movement axis of the guide rail and the optical axis of the primary and secondary mirrors. The consistency debugging of the optical axis was completed through two parts: initial adjustment and fine adjustment. The initial adjustment realized that the primary and secondary mirrors were basically located in the theoretical installation position, reducing the adjustment errors. Then, the computer-aided adjustment was performed to achieve precise adjustment of optical axis consistency of the primary and secondary mirrors, so that the system wave aberration met the requirements. The experimental results show that the wave aberration root mean square (RMS) of the infinitely distant system reaches (1/15) λ (λ=632.8 nm), the system has a diffraction resolution of 0.64", and the system is focused to 10 mm. The measured focal length of the primary and secondary mirror system is 1 608 mm, and the system resolution reaches 2.6", which meets the design requirements.