The properties of a QCW LD pumped Yb:YAG microchip laser was first presented in detail. At room temperature, 1 64 mW average output power and 16 4 μJ pulse energy at 1 049 μm were obtained with a 10 at % doped Yb:YAG microchip crystal when diode current was at 2 15 A. The beam quality factor M 2 values were measured to be 1 37 and 1 15 in the vertical and horizontal directions respectively. Theoretical results of laser output pulse width and relaxation oscillation were consistent with experimental values by analysis of quasi three level rate equations of Yb:YAG microchip laser.