A high-power multi-pass-pump Yb∶YAG planar waveguide laser amplifier was designed. The new amplifier adopted symmetrical pumping scheme, in which the pump sources were symmetrically placed on both sides of the planar waveguide. The pump light, reflected in the planar waveguide, passed through the core multiple times. Multi-pass pump was thereby achieved. The factors affecting the pump absorption characteristics were analyzed, and the relationships between the geometric parameters of the planar waveguide were determined. The planar waveguide structure was optimized. The pump absorption, temperature, and output amplification characteristics of the planar waveguide amplifier were analyzed by a laser amplification model. The results show that the designed multi-pass-pump planar waveguide amplifier has high pump absorption and optical-to-optical efficiencies. When the power of the injected seed light is 200 W and the pumping power is 10 kW, its maximum pump absorption efficiency is 96.8%, with a corresponding amplified output power of 7483 W and an optical-to-optical efficiency of 72.8%. Meanwhile, a good absorption uniformity makes the amplifier less affected by the heating effect, which is beneficial to obtaining high-quality beams.