A diode-pumped tunable Yb∶YAG thin disk laser was studied. Tuning wavelength range from 1020.5 nm to 1034.7 nn was obtained by using a quartz-birefringent filter set in the laser cavity. And the generation of 515 nm green laser was demonstrated by intracavity frequency doubling of type-I phasematched LBO in a fold cavity. A CW output power of 2.5 W at 515 nm was achieved. The fluctuation of green laser was less than 1% at the maximum output power in 1 hour.