Phase change films with SiN/Sb80Bi20/SiN structure are deposited on the K9 glass substrates by direct current magnetron sputtering. Nonlinear optical response of transmittance and reflectance of the films is investigated using a confocal Z-scan technique with a continuous wave He-Ne laser. The results indicate that the transmittance and reflectance at focus both have nonlinear response induced by phase change. The transmittance at focus increases with the increasing of scan power and keeps a saturated value. Formation of phase change micro-area can be achieved at focus of scan laser,and the area will increase with the increasing of scan power. The transmittance of irradiated sample under different powers was studied with in situ repetitive method;and the repetitive power is smaller than the phase change threshold. The results of repetitive Z-scan experiments indicate that the phase change area have a good opto-thermal stability. BiSb films show potential capability for phase change data storage.