The invention relates to a rainwater drainage control device used for controlling the initial rainwater drainage of a rainwater collecting device. The rainwater collecting device comprises a water collecting unit, a water storing unit, a rainwater feeding pipe transferring rainwater from the water collecting unit to the water storing unit, a rainwater collecting pipe communicated with the water storing unit and a drainage pipe arranged between the feeding pipe and the collecting pipe. The initial rainwater automatic drainage control device controlled by the rainfall comprises an raingauge, an electric valve arranged on the inlet of the rainwater collecting pipe and a controller which controls the opening and closing of the electric valve on the rainwater collecting pipe according to the comparative result between the measured rainfall by the raingauge and the expected drainage so as to realize the automatic control to the initial rainwater drainage. The initial rainwater automatic drainage control device controlled by the rainfall also comprises a device used for regulating the expected drainage and a device used for setting the non-drainage rainfall intervals so as to effectively reduce the drainage, and a level sensor used for leading the controller to control the level of the water storing unit according to the signal sent by the level sensor.