A high peak power Nd∶YAG laser system with moderate repetition rate is demonstrated. The laser system contains three main components, the all-fiber-based seed, LD-pumped Nd∶YAG regenerative amplifier and flashlamp-pumped two-pass Nd∶YAG amplifier. The average power is 12 W, the repetition rate is 10 Hz, the single pulse energy of the laser system is up to 1.2 J, and the pulse width is 3 ns. With the wavelength of 1064 nm, the diameter of the output beam is 10 mm. More than 95% pulse energy is focused in the range of 600 μrad.The beam intensity distribution is near top-hat in the near filed and the intensity modulation is less than 1.2. The temporal pulse shape is square-pulse. The root mean square value of the pulse energy is less than 1.4%.