High efficiency and high average power nanosecond pulsed solid state lasers are playing an increasingly important role in photoelectric countermeasures, lidar, material modification, laser processing and many other fields. However, at present, Yb:YAG or Nd-doped materials are adopted as gain medium in most nanosecond high average power lasers. The high saturation flux or low energy storage density of the materials lead to complex laser amplification link and large laser volume. In this paper, a disordered garnet crystal Yb:CNGG that is more suitable as a gain medium for high average power and high pulse energy lasers is studied and compared. The multi-pass gain characteristics of Yb:CNGG in the structure of active mirror are researched. The amplification process is analyzed and the multi-pass amplification model is established. The crystal parameters are optimized under certain pumping conditions to achieve better energy storage. The double-pass amplification experiment was carried out, and a gain of 1.53 was obtained at the pump power density of 15 kW/cm². The multi-pass amplification capability of Yb:CNGG and Yb:YAG is compared. Under the same crystal parameters and pumping conditions, the pulse energy output of 2.11 J can be achieved by Yb:CNGG crystal at the incident energy of 1 mJ, which is better than the energy output of 1.41 J of Yb:YAG crystal.