A compact diamond window cooled Yb^{3+/SUP> ∶ YAG disk laser has been demonstrated. In this cooling scheme,the rear face of disk is cooled directly by water while the front face of disk is applied in good thermal contact to a thin plate of chemical vapor deposition diamond window. The exceptionally good heat conduction properties of diamond can eliminate the temperature gradients perpendicular to laser beam thus previous difficulties with high average power pumping and efficient cooling are resolved. Simulation results show that with a pump intensity of 20 kW/ cm2 and repetition rate of 10 Hz,to keep the maximum temperature of the gain disk below a reasonable value,e. g.,less than 320K,the heat exchange coefficient of water should be about 4000 W/m2 K.}