We develop a compact and high-energy Nd:YAG slab laser system consisting of an oscillator and an amplifier for space applications. The oscillator is a diode-side-pumped electro-optically Q-switched slab laser with a cross-Porro resonator. The KD*P Pockels cell with a low driving voltage of 950 V is used to polarization output coupling. The amplifier is a Nd:YAG zigzag slab pumped at bounces. The maximum output pulse energy of 341 mJ with 13 ns pulse duration is obtained from the system at the repetition rate of 20 Hz and the beam quality factors are M 2 x = 3.1 and M 2 y = 3.5. The beam pointing stabilities of the laser system are 3.05 μrad in the X-direction and 3.99 μrad in the Y-direction, respectively.