In the traditional infusion process, medical staff need to regularly observe the change of liquid level in the infusion bottle to confirm the dressing change time, which not only increases the workload of medical staff, but also increases the risk of emergency. In this paper, a kind of infrared automatic alarm device based on AT89C51 MCU is designed, which can monitor the liquid level change in infusion bottle in real time and remind medical staff to replace infusion set in time. According to the principle of infrared positioning and monitoring, the device collects the liquid level information in real time and gives an alarm when the liquid level is too low. Proteus software is used to simulate the whole control system. Through analysis, it is found that when the liquid level of the infusion set is too low, the infrared signal waveform changes, so the automatic alarm device has a high accuracy.