The invention discloses an electronic control device, which is installed in the bulk of liquid heater and connected with the electrical circuit while working independently. It includes: signal collection module, signal analysis module and electrical switch module, which connects each other electrically in turn. The signal collection module collects temperature information and transforms them into electrical signals. The signal analysis unit receives the above electrical signals, transforms them into control ones and sends to the electrical switch module. In addition, the invention provides a liquid heater with the electronic control device.