A laser diode array (LDA) with the micro-lens two-side-pumped Yb:YAG slab laser was reported, the Yb:YAG slab was in size of 6 mm×10 mm×1 mm, and the doping concentration was 3 at.-%. A novel structure was designed to focus the pump beam to as small as 10 mm×1 mm in size. The transmission efficiency of the structure is about 75% and the pump intensity could be reached as high as 1.9 kW/cm2 on the surface and 38 kW/cm3 in the bulk that is more higher than the threshold of 1.7 kW/cm3. The maximum output pulse energy of 25.5 mJ with slope efficiency of 13% was obtained from a plano-concave cavity with an output coupling of 6%. Once an acousto-optic modulator (AOM) was inserted into the cavity, Q-switched pulse with energy of 4.7 mJ and pulse width of 24.8 ns were achieved.