Abstract: The present invention relates to a roller blind and a control device thereof. The control device comprises a reeling mechanism, a solenoid valve, a push mechanism, a front cap, and a damper. After the solenoid valve is energized, the solenoid valve drives the push mechanism to push against the front cap so as to separate the front cap from an engaging portion of the reeling mechanism, and the reeling mechanism is not subject to a resistance of the damper. A curtain fabric is not affected by the resistance of the damper and can be quickly lowered by gravity.