An operation method for a portable electronic device is provided. The portable electronic device includes a micro-controller, a ringing module, a g-sensor and an image capturing module. The operation method includes the following steps. When the ringing module is started up at a pre-set time, the g-sensor detects whether the portable electronic device is slanted. If the portable electronic device is slanted, the micro-controller enables the image capturing module to perform human-eye recognition. If human-eye recognition is performed successfully and lasts for a specific period, the micro-controller disables the ringing module.