An intra-cavity frequency doubled Yb:YAG/BIBO 515 nm thin disc laser is demonstrated. The Yb:YAG crystal with 10% doped concentration is 420 μm in thickness and 11 mm in diameter. It is mounted onto the micro-channel copper heat sink by Cr/Au/In.The pump light absorption and pump beam radius are calculated. A four-pass optical coupling system is well designed with two spherical imaging mirrors with diameter of 26 mm and curvature radius of 50 mm. A 3 mm×3 mm×2 mm BIBO crystal cutting at a type-I phase-matching direction of (θ，Φ)=(166.7°，90°) is employed. With 24.9 W incident pumping power, the maximum output power of 680 mW at 515 nm is obtained. The optical-optical conversion efficiency is 2.73%.