An Er,Yb∶glass slab amplifier pumped by laser diode (LD) array is designed in this paper, which adopts a multi-bounce structure to improve extraction efficiency. It is expected to achieve the laser output with greater energy in the 1.5 μm band, and the laser amplification gain can reach 35.29. Based on the steady-state heat conduction theory, the thermal effect of the Er,Yb∶glass slab amplifier is analyzed and the thermo-mechanical coupling model is established. The thermodynamic characteristics of the slab medium at different parameters are compared by the finite element method. The results indicate that the thermal effect can be effectively alleviated by increasing the width-thickness ratio of the slab and reducing the power density of the pump light. Based on the analysis, a method for wavefront distortion compensation is proposed.