The invention discloses a continuous rainwater precipitating and separating device and a control method thereof. The continuous rainwater precipitating and separating device comprises a sludge collecting device, a sludge discharging pipe, a clear water collecting device, a water draining pipe, a support pillar, a water conveying tank, a movable rotation shaft, a support frame, a support rod, a precipitating and separating barrel and a clear water collecting barrel, wherein the clear water collecting device is arranged on one side of the sludge collecting device; the support pillar is fixed in the clear water collecting device; the support rod is arranged on the support pillar via the movable rotation shaft; the support frame is arranged on the support rod; the water conveying tank is arranged on the support frame; one end of the support rod is connected with the precipitating and separating barrel; the other end of the support rod is connected with the clear water collecting barrel. A control method of an automatic rainwater precipitating and separating device comprises a water collecting and precipitating stage, a precipitating and draining stage, a clear water collecting stage, a water collecting and draining stage and a sludge discharging stage. The continuous rainwater precipitating and separating device is small in occupied area, simple in process and simple to operate and is capable of instantly collecting, separating and precipitating the rainwater, so that the loss of the water resource and the pollution to the water resource are reduced; the device is high in mechanical automation degree; the rainwater recycling rate is high; the high water quality is guaranteed.