A pump-probe system is employed to observe transient reflectivity change process of Bi20Sb80(BiSb) films induced by picosecond laser pulses. Spectroscopic ellipsometry and atomic force microscopy are used to study the micro-area optical properties and surface structures of irradiated areas. Experimental results indicate that fast and recoverable switching can be achieved on BiSb films induced by single-shot or repeated picosecond laser pulses with a proper pumping fluence. The switching time is about 19 ns, which is independent on the laser fluences. The BiSb film is shown to be very promising for ultrafast super-resolution mask layer. These results are helpful for developing new mask layer materials with fast optical response and understanding the working mechanism of BiSb super-resolution mask layers.