Abstract: To fill the theoretical gap of the property distortion mechanism of supercritical fluids, the molecular dynamics simulation at the micro scale, mean field theory and scale theory at the mesoscopic scale, and property measurement experiments at the macro scale were analyzed. The molecular dynamics simulation was used to obtain the microstructure characteristics of carbon dioxide system when crossing pseudo-critical points, and the molecular dynamics mechanism of property distortion was obtained by analyzing the variation law of structural parameters such as pair radial distribution function. The simulation result proves the existence of gas-like region, liquid-like region and the rapid transitions between them. Based on Landau theory and scale theory, a new model was proposed to quantitatively predict the distortion laws of thermodynamic quantities such as density and isobaric specific heat of supercritical fluids near the pseudo-critical region and approaching the critical point. Compared with the classical Landau theory, the new model is based on a redefined order parameter η and adds a first order term of η. This term represents the effect of the external field on the thermodynamic potential, and also corresponds to the effect of temperature and pressure on the fluid system. At the macro scale, high-precision measurement experiments of density, isobaric specific heat and viscosity of supercritical carbon dioxide was carried out, and the potential defects of existing models were pointed out in this paper. The accuracy of the existing thermodynamic property calculation models of carbon dioxide are good outside the pseudo-critical region, but there are still defects inside pseudo-critical region or near the critical point. Moreover, the calculation accuracy needs to be verified by experiment and further improved. The results show that for different supercritical fluids, there is a general law of property distortion near the critical point and in the pseudo-critical region. On the phase diagram, the supercritical fluid region can be further divided into four regions: The vicinity of the critical point, gas-like region, liquid-like region and pseudo-critical region. In different regions, the characteristics of supercritical fluids are dominated by the laws at different scales. In the vicinity of the critical point, the fluctuation within the system plays a dominant role, which leads to the inapplicability of both mean field theory and continuum hypothesis. Therefore, the study of fluid in this region must start with more basic assumptions, based on molecular dynamics simulation or lattice Boltzmann method. However, the vicinity of the critical point is so small that the classical descriptions are valid in most conditions.