Nd: YAG ceramics have the characteristics of large size and low cost, but the mode-locked laser based on Nd:YAG ceramics has not been widely verified. Using Nd:YAG ceramic as gain medium and semiconductor saturable absorption mirror (SESAM) as mode-locked element, the W-type resonator is optimized. When the pump power is 11.49 W, 1.25 W stable mode-locked laser with laser wavelength of 1.06 μm and repetition frequency of 144 MHz is generated. The pulse width of the mode-locked laser is 33.6 ps, the single pulse energy is 8.7 nJ, and the peak power is 0.26 kW. The experimental results show that Nd:YAG ceramics can be used as gain medium in passively mode-locked ultrafast picosecond lasers.