The working principle of fax machine is very simple, that is, the document to be sent is scanned and converted into a series of black and white dot information, and then converted into audio signals, which are transmitted through traditional telephone lines. After the receiver's fax machine "hears" the signal, it will print out the corresponding point information, so that the receiver will receive a copy of the original.

The fax machine decomposes the original to be sent into many tiny units (called pixels) by the optical scanning system in a specified order, and then the brightness information of these tiny units is converted into electrical signals by photoelectric conversion devices in turn, which are amplified, encoded or modulated and sent to the channel. After amplifying, decoding or demodulating the received signal, the receiver copies the original in the form of recording at the same scanning speed and order as the transmitter.

Thermal paper fax machine (also known as network fax machine): Thermal paper fax machine melts and discolors the thermal materials on the printing medium through the thermal print head to generate the required text and graphics. Thermal transfer printing is developed from thermal technology. By adding a thermal transfer ribbon, the ink coated on the ribbon is transferred to paper to form an image. Thermal printing is used in the most common fax machines.

Laser plain paper fax machine (also called laser all-in-one machine): Laser plain paper fax machine is a fax machine that uses toner to attach to paper and images. Its working principle is to use a selenium drum in the machine body to control the laser beam. By controlling the on and off of the laser beam, a charged image area is generated in the selenium drum. At this time, the toner in the fax machine will be attracted by the charge and attached to the paper to form words or images.