A method of automatically switching in an on-hook state suitable for a telephone system is provided. The method automatically switches a spring circuit from an off-hook state to the on-hook state when the telephone system operates in an abnormal use state for a unreasonably long period of time. Therefore, the telephone system can be switched back to the on-hook state when the mouthpiece is unintentionally off the hook so the missing of the phone call can be effectively avoided.