A control method and system for a belt-driven clothes dryer are disclosed. The control system includes a drum containing a load of wet clothes to be dried, a heater heating air flowing into the drum, a motor coupled to the drum by a power transmission system for rotating the drum, and a power supply supplying power to the motor and the heater during a dry operation of the dryer. The control system further includes a moisture sensor outputting a sensor signal during the dry operation, or a photo coupler outputting voltage pulses when the motor is in operation during the dry operation. Then, a microprocessor included in the control system detects a breakage of the power transmission system upon analyzing the sensor signal of the moisture sensor or the voltage pulses generated by the photo coupler. If the microprocessor detects such breakage, it interrupts the dry operation of the clothes dryer.