For the requirements of compact and simplified solid laser gain module structure design, a model of Nd∶YAG crystal rod unilaterlly pumped by laser diode (LD) stacked array is built. The absorbed light distribution within the Nd∶YAG crystal rod in ceramic condenser chamber is simulated with the TracePro software. The influences of condenser chamber′s shape, crystal rod′s radius and doping concentration of Nd3+ on the light collecting efficiency and the gain distribution uniformity are studied. The research shows that the light collecting efficiency changes approximately linearly with the cross-sectional area of the condenser chamber. A Nd∶YAG crystal rod with radius of 2 mm and Nd3+ doping concentration of 0.5% (atom fraction) can obtain near fundamental mode oscillation output with 1.0 mm spot radius. The distribution of absorbed pumping light is more uniform when the ratio of the uniform pumping area radius of crystal rod to the U-shape condenser chamber radius is about 0.5. With the discussed structure, the light collecting efficiency reaches 65%, while the gain distribution uniformity is better than 0.65 in the LD stacked array unilaterally pumped Nd∶YAG crystal structure.