The invention discloses an initial rainwater runoff control device, which comprises a controller, a runoff collection pipe and a rainwater collection hopper, wherein, an electromagnetic valve connected with the controller is arranged in the runoff collection pipe; the lower end of the rainwater collection hopper is provided with a first rainwater monitoring hopper and a second rainwater monitoring hopper; a first floating ball, a first water outlet, a first overflow port and a first water level probe are arranged in the first rainwater monitoring hopper; a second floating ball, a second water outlet, a second overflow port and a second water level probe are arranged in the second rainwater monitoring hopper; and the first water level probe and the second water level probe are respectively connected with the controller. Compared with the prior art, the device adopts a microcomputer control technology and has a control principle different from other devices; the microcomputer control has good stability, high accuracy, convenient operation, practicability and safety, and has greatly improved environment adaptability compared with the prior device; in addition, a microcomputer has lower power, so the device is more environment-friendly and energy-saving.