A Nd∶YAG composite ceramic slab end-pumped with diode is designed theoretically, and a dual concentration doped Nd∶YAG composite ceramic slab is fabricated. The extracted power after double-pass amplification is 7.08 kW when the total pumping power of diode is 18.06 kW, the optical-optical conversion efficiency is up to 39.2%, and the depolarization of single-pass transmission is about 3.2%. The experimental results show that the Nd∶YAG composite ceramic slab has significant effect on enhancing the output power and reducing the depolarization of the slab laser.