The invention discloses a supercritical CO2 waterless dyeing system and a cloth dyeing method thereof. The method comprises the following steps of A, preparing and storing of CO2; B, cooling; C, pressurizing; D, heating, wherein a heating device is utilized for enabling CO2 to form supercritical fluid, and the supercritical fluid is heated to 120-150 DEG C; E, dyeing, wherein a circulating pump pushes a mixture of the supercritical fluid and dye to circularly flow inside a circulation channel, cloths inside a pressure kettle are dyed, the pressure inside the pressure kettle is 28-30 MPA, the temperature is 120-150 DEG C, the circulation flowing time is 20-40 min, and the circulation flow is not smaller than 10 M<3> per hour; F, pressure relieving, wherein a nanoscale color masterbatch is dissolved through the supercritical CO2 fluid, the cloths are dyed, and dyeing technological conditions such as pressure, temperature and time are optimized at the same time so as to improve the dyeing efficiency and dyeing quality.