A liquid supplying device for a human insulin injection includes a substrate, a liquid storage chamber, a flow-guiding-and-actuating unit, a sensor and a driving chip. The flow-guiding-and-actuating unit includes a liquid guiding channel having a liquid guiding outlet in fluid communication with a liquid storage outlet of the liquid storage chamber. The sensor contacts with the human skin to measure a blood glucose level contained in sweat. The driving chip is configured to control the actuation of the flow-guiding-and-actuating unit, control open/closed states of the switching valves and receive the measured data from the sensor for determination. By driving the flow-guiding-and-actuating unit, a pressure gradient is generated, and an insulin liquid stored in the liquid storage chamber is transported to the liquid guiding outlet through the liquid guiding channel, flowing into a microneedle patch, and injected into a subcutaneous tissue through a plurality of hollow microneedles.