The system uses PIC16F886 MCU as microcontroller and ultrasonic detection as core technology to design the medical ultrasonic oxygen flowmeter, within MPLAB software system.This system mainly consists of PIC MCU module, the signal switching circuit, the analog amplifier circuit,the filter circuit and the voltage comparison circuit. Oxygen is sent through a fixed pipeline, then the microcontroller send signals to the ultrasonic transducer, to measure the transit time of ultrasonic flow and temperature of oxygen.Based on least squares surface fitting method, we set up the oxygen concentration as a function of temperature and time, completing the measurement of gas flow.The measurement results show that the system is stable and reliable,and has high precision and very high value for engineering use.