Abstract: The thermoplastic polyurethane (TPU) foam is prepared by one-step pressure relief method using supercritical CO2 as foaming agent. The hard-segment (HS) crystallization and foaming behavior of TPU assisted by CO2 are studied by differential scanning calorimetry (DSC) and scanning electron microscopy (SEM). The results indicate that, the polydispersity HS formed during blend process is beneficial for crystallization. And a more perfect crystal can form with higher foaming temperature and pressure. Furthermore, more crystals can be gained with elevated foaming pressure and the microporous foam is obtained when the pressure reaches 20MPa