Objectives Carbon monoxide is an important messenger molecule in the human body, which can be used for the treatment of neonatal pneumonia, neonatal hypoxic-ischemic encephalopathy and other serious diseases. In order to explore the use of CO inhalation in the treatment of these diseases, a carbon monoxide inhalation device based on a mass flow controller is developed in this paper. Methods The mass flow controller in the device controls the flow of CO gas according to the calculated flow value of CO and delivers it to the respiratory circuit. At the same time, the concentrations of CO are detected by the electrochemical CO sensors before the therapeutic gas enters into the patient.It can provide the function of real-time monitoring and dynamic display of concentration.The actual value of CO concentration is fed into the main control circuit, by which a PID algorithm can continuously adjust output flow of the mass flow controller to maintain accurate concentration of CO in the treatment gas. And the indication error, the response time, the repeatability error, the stability error and so on are tested by the experiment with the ventilator. Results The indication error of the device is 0. 98%, the response time is 30 s, and the relative standard deviation and relative error are 0. 24%and 2. 07% respectively. Conclusions The indication error of the carbon monoxide inhalation device, repeatability error, response time and stability of the error system meets design requirements, provides a safe and reliable method for the clinical treatment of inhalation of CO.