The invention discloses a liquid level control device which comprises a support, a cylindrical buoyancy block and a support fixing seat. The upper portion of the support is connected with the upper end of the support fixing seat, the lower portion of the support fixing seat is connected with a base, a front connecting plate and a rear connecting plate are arranged on the lower portion of the support, connecting holes and a connecting shaft are arranged on the front connecting plate and the rear connecting plate, the rear end of the cylindrical buoyancy block is hinged to the connecting shaft, an upper inner cavity and a lower wire hole are formed in the front end of the cylindrical buoyancy block, the lower wire hole is communicated with a radial wire hole of the buoyancy block, a floating ball switch is arranged in the inner cavity, a lower cable of the floating ball switch stretches out of the lower wire hole and the radial wire hole, a lower limiting baffle is arranged at the lower end of the support, an upper limiting baffle is arranged on the upper portion of the support, and the lower limiting baffle, the upper limiting baffle and the cylindrical buoyancy block are matched in position. The liquid level control device is simple in structure, the motion of the floating ball switch is reliable, the liquid level control device is suitable for occasions with poor environment, such as occasions including oil, emulsified liquid and sludge waste water, and waste water is prevented from flowing outside to cause environmental pollution and personal injury accidents.