Water level sensor and operation method of clothes dryer with liquid injection module

The present invention relates to an operation method of a clothes dryer. The clothes dryer comprises the following components: a liquid injection module which injects liquid into a tumbling cylinder; and a water level sensor which is used for detecting the water level of the liquid stored in the liquid injection module. The operation method of the clothes dryer comprises the following steps: a detection step of detecting the water level once a drying process comprising liquid injection is selected; a notification step of displaying the low water level state to outside when a low water level is detected in the detection step; and a process execution step of sustaining the low water level display state and executing the selected drying process once a starting button of the selected drying process is pressed.