The invention relates to a serial port to Ethernet control device based on STM32. The control device comprises: a power supply circuit, a micro-control unit circuit, a JTAG debugging interface circuit, a serial port communication interface circuit and an Ethernet physics interface transceiver control circuit. The power supply circuit comprises: a power supply voltage stabilization chip, a double pin power supply connector, a rectifier diode, a light emitting diode, an inductor, a chip resistor, two tantalum capacitors and four ceramic capacitors. The micro-control unit circuit comprises: a STM32 interconnectivity processor, an expansion pin, a crystal oscillator, two buttons, the three chip resistors and the eleven ceramic capacitors. The Ethernet physics interface transceiver control circuit comprises: an Ethernet physics interface transceiver control chip, an RJ45 interface, an active crystal oscillator, the tantalum capacitor, the sixteen chip resistors and nine ceramic capacitors. The control device has advantages of a small volume, low costs and low power consumption. And telnet can be achieved so as to perform real time operation and monitoring.