According to Enforcement Rules of the Occupational Safety and Health Act, a business unit has to detect carbon dioxide concentration in some workplace. It is often being questioned that whether this detection is necessary or not, because the detecting result shows that the carbon dioxide concentration is always under the standard. Although there are some arguments in carbon dioxide concentration assessment, the labors are familiar with the information about carbon dioxide. Therefore, it still needs to be discussed and taken it seriously. This research uses experiment to discuss the meaning of carbon dioxide assessment and its´ application, and combining with legislation and literature to discuss the expected meaning of carbon dioxide. Otherwise, this research also offers a business unit as an operating environment reference that how to do carbon dioxide assessment and turn the research result into another meaning in the regulation of carbon dioxide assessment. This study tests a special situation in a long time, including in some particular place and simulation chamber, and observes the changing of carbon dioxide concentration. By following the changing of carbon dioxide concentration, it can confirm the notice of carbon dioxide assessment again. At last, combining with research data and literature, and discuss that how to use this assessment result to prove operating environment. The research shows that assessment data of carbon dioxide can be influenced when changing time and space. It should be formulated an appropriate strategy and it may be shown a meaningful result. Normally, the data of carbon dioxide assessment was defined by the accumulation of carbon dioxide that employee breathe in working place. In literature, the highest carbon dioxide concentration is 3,300 ppm, and the average carbon dioxide concentration is 2,250 ppm in the student classroom. It shows that the lone time average carbon dioxide concentration will not be over 5,000 ppm, and we can forecast that in working place may have the same result. It’s meaningful that concerning another source of carbon dioxide in working place without employee’s breathing, and it also can connect with assessment data and the standard of concentration. The other thing is carbon dioxide can be used that understanding labors’ operating environment, and manage working place ventilation. If the concentration is over the standard, the business unit has to do carbon dioxide assessment again to make sure that whether the rate of exchange fresh air is corresponded with the standard.