The invention discloses an automatic emission control system based on a calcium carbonate sedimentation tank. The automatic emission control system comprises a slurry input pipe, a calcium carbonate sedimentation tank, a sediment discharge pipe, a clear liquid discharge pipe, a solenoid valve and a master control module. The slurry input pipe, the sediment discharge pipe and the clear liquid discharge pipe all communicates with the calcium carbonate sedimentation tank. The solenoid valve is installed on the sediment discharge pipe and also connected to the master control module. A certain timeinterval is set by the master control module in order to switch on the solenoid valve for a certain time and timely and automatically discharge the calcium carbonate sediment at the bottom of the calcium carbonate sedimentation tank. Therefore, not only is the trouble of manual operation is reduced, but also the calcium carbonate sediments are discharged timely to ensure the system's operating efficiency.