To analyze the structure and thermo-regulated performance of Outlast viscose fiber, the fiber structure was observed respectively by FTIR spectra, X-ray diffraction and scanning electron microscope, and the thermo-regulated performance was investigated by differential scanning calorimeter, thermal gravimeter analysis and step cooling test. The results indicate that the structure of Outlast viscose fiber is similar to that of normal viscose fiber. Both the melting peak and crystallization peak of Outlast viscose fiber are double peaks, and the phase change temperature range is applicable and the phase change enthalpy is high. The decomposition temperature of Outlast viscose fiber is about 280-320°C. The cooling velocity of Outlast viscose fiber decreases exponentially with the increase in time, and the thermo-regulated ability of Outlast viscose fiber is better than that of normal viscose fiber.