We study the packaging method and key technologies of thin-disk laser, and report on our home-made thin-disk module comprising a YAG/Yb∶YAG composite thin-disk crystal with 5 mm diameter, which is glued onto a diamond heat sink. The multi-pass pumping scheme of the thin-disk module is analyzed and a numerical simulation model of thermal effect is established. The thermal focal length of the thin-disk crystal is measured to be approximately 445.6 mm at pump power density of 2.2 kW/cm² and pump wavelength of 940 nm. A continuous wave laser based on the thin-disk module is realized and it delivers fundamental mode output of 18.75 W at the pump power of 70 W. The slope efficiency and optical-to-optical efficiency are 36.59% and 26.79%, respectively.