The invention relates to a turntable bearing for a large-size celestial observation device, comprising an outer ring (1), an O-shaped seal ring (2), a holder (3), a large ball (4), a small ball (5), a round clamp (6), an inner ring (7), a dust shield (8) and a round baffle plate (9). The turntable bearing adopts a double-reduced ball structure and a large contact angle structure, the large ball and the small ball respectively bear axial and radial load and ensures the axial rigidity of the turntable bearing, and the small ball adopts a straight-raceway full ball structure, increases radial carrying capacity and satisfies the requirements of a low friction moment simultaneously; the dust shield and the O-shaped seal ring are adopted to seal, a raceway contact point is provided with a radial lubricating hole to indirectly lubricate the turntable bearing, and the turntable bearing can be more sufficiently lubricated and has better lubricating and sealing performance. When the turntable bearing is installed, a bracket shaft is matched with a smallest spigot of the inner ring and is fixed on a bracket (11), and a rotating table (10) is fixed on the spigot of the upper end of the outer ring to regulate a direction angle.