A supercritical carbon dioxide state monitoring and control system based on infrared spectrum characteristic analysis. The system includes: a test section for carbon dioxide to pass through; an infrared light source emitting a detection beam to the carbon dioxide passing through the test section; an infrared spectrometer receiving and analyzing the detection beam passing through the carbon dioxide; and a pressure control module controlling pressure of the carbon dioxide at a set value. In addition, the system also includes a temperature control module capable of monitoring and adjusting temperature of the supercritical carbon dioxide. The supercritical carbon dioxide state monitoring and control system may monitor and control a state of the carbon dioxide at an inlet of an apparatus under an actual operation condition in a Brayton cycle system, which improves working performance of the apparatus in the Brayton cycle system, thereby improving overall efficiency of the Brayton cycle system.