The invention discloses a method for controlling the speed of a cooling roller bed after rolling a medium plate, which belongs to the technical field of steel rolling automatic control, is mainly used in the process of cooling the medium plate after rolling, and realizes the control of the cooling uniformity of a steel plate in the length direction by controlling the speed of the roller bed. The invention provides the method for controlling the speed of the cooling roller bed after rolling the medium plate, which can ensure the cooling uniformity of the steel plate in the length direction. The method adopts a cooling control system after rolling and comprises the following steps: firstly, performing sample division on the steel plate in the length direction; secondly, before the steel plate enters an activation cooling zone, acquiring the actual temperature value of the steel plate in the length direction through a thermo-detector before cooling, and determining the speed of each sample of the steel plate to pass through the activation cooling zone; and thirdly, transmitting the speed, determined in the second step, of each sample of the steel plate to pass through the activation cooling zone to a basic automation unit of the cooling control system after cooling, and controlling the speed of the cooling roller bed by the basic automation unit of the cooling control system after cooling.