A laser preheating control method is applied to a laser preheating control device. When a cutter processes a workpiece along a process path, a laser source of the device is provided to output a laser beam to the workpiece for selectively forming a laser spot on the workpiece surface. And according to a movement direction of the cutter, a laser controller of the device is provided to form the laser spot only on a preheating region of the workpiece, where in front of the cutter in the process path, for preheating the workpiece in the preheating region. As a result, the laser spot will not repeatedly heat the workpiece behind the cutter in the process path, and the qualitative change of the workpiece caused by repeating heating is preventable.