The interrelations between the parameters of VRM and Cassegrain unstable resonator and their effects on laser intensity distributions are studied in this paper. The experimental results of Nd∶YAG laser using VRM output coupler are presented in detail. Up to 1.4 J TEM 00 mode output pulse (10 ns, 10 pps) with 1.1 diffraction limited divergence can be obtained by using VRM unstable resonator and one amplifier. The effeciency of SHG is 60% and THG is 30%.