To develop a compact laser with high power as well as good beam quality，a composite Nd∶YAG/YAG transparent ceramic polygonal active mirror gain medium structure is reported，and conceptual validation is conducted by researching the laser output characteristics. The composite Nd∶YAG/YAG transparent ceramics used in this work are fabricated by the transparent ceramic technique. The five sides of the polygonal active mirror are Nd∶YAG doped regions，which are also laser gain mediums. The optical properties of the composite Nd∶YAG/YAG ceramics and the laser performances of polygonal active mirror are investigated. With a pump power of 4.05 W，a maximum output power of 0.43 W is obtained，and the corresponding optical-to-optical and slope efficiencies are 10.6% and 16.9%，respectively. The corresponding beam quality factors are and The results of this study demonstrate the feasibility of using transparent ceramic techniques to fabricate laser gain mediums with functional structures，which brings more flexibility to the design of lasers.