A method and device for measuring the concentration of medical expiratory carbon dioxide are provided. The method includes arranging three measurement windows on a chopping disk; sealing a carbon dioxide standard gas of a known concentration in one of the windows; arranging the chopping disk on a light path; dividing a one-passage light path into three measurement passages through the three windows; feeding a carbon dioxide gas having a known concentration; setting a preset number of calibration points; establishing a carbon dioxide concentration value table according to the relationship between carbon dioxide concentrations and light transmitting intensity; and searching the table, and acquiring a real-time measurement value of the medical carbon dioxide through calculation. Only one signal amplification passage is needed in the three measurement passages as the chopping disk is adopted, thus saving the cost. When the method and the device are applied for zero point correction, zero point correction can be performed with the known carbon dioxide standard gas concentration without the need of introducing outer air as a zero point reference, thus achieving a function of no zero correction and improving measurement stability.