The invention discloses a swing arm balancing and driving mechanism. The swing arm balancing and driving mechanism mainly solves the problems that sprue gates need to be manually blocked after existing castings are poured and the operation is dangerous. The swing arm balancing and driving mechanism is characterized in that a rotating shaft (7) is fixed to a base (3) and connected to a horizontal swing arm (6), the swing arm (6) is divided into a long arm (6-1) and a short arm (6-2) with the rotating shaft (7) as the center, a motor support (5) is fixed to the short arm (6-2), a motor (1) is fixed to the outer side of the motor support (5), an output shaft of the motor (1) is connected to a gear (2), the gear (2) is meshed with a fan-shaped gear (4), the fan-shaped gear (4) is fixed to the base (3), and a sprue gate blocking device (8) is fixed to the left end of the long arm (6-1). The swing arm balancing and driving mechanism adopts the mechanical device for blocking the sprue gates, can reach the work position when needing to work and leave the work area when stopping working, and is convenient to operate, safe and reliable.