The experiment research and academic analysis on high power slab laser end-pumped with laser diode arrays (LDA) are developed, and the steady laser power output of the thin slab laser is achieved in resonator with 4f system. The continuous-wave laser with average power of 3.24 kW is achieved through plano-concave resonator when the injecting power approaches to 10 kW. The loss coefficient of the laser resonator and the diffraction loss of the slab end are obtained indirectly by measuring the saturated gain coefficient of the laser medium when the laser output power is steady. The influence of the overlap factor on the laser power is analyzed, and the experimental results provide the basis for the optimization design to high power slab lasers.