The theoretical research on the Yb…YAG laser pumped by the zero-phonon line with pumping wavelength of 969 nm is constructed, and the rate equations for this 969 nm pumped Yb…YAG laser are established. The optical-to-optical efficiency and the output laser intensity of this Yb…YAG slab laser amplifier pumped at 969 nm or 941 nm are obtained by numerical simulation under the same thermal load state. The simulation results show that the optical-to-optical efficiencies for both are almost equivalent. The pumping intensity for 969 nm pumping is 20% higher than that for 941 nm pumping.