La_Sr_Cu_O thin films on Si(100) substrates have been grown by pulsed electron beam deposition technique.The thin films obtained have been characterized by x_ray diffraction (XRD),scanning electron microscope(SEM),energy dispersive x_ray analysis (EDX) and focusing ion beam (FIB) technology.Highly ordered surface nanostructure has been found.FIB technology has been used to characterize those nanostructures.The nanostructure was cut by FIB,and its cross section can be seen clearly also.The nanostructure was etched by FIB step by step,and the depth_resolved morphology was shown.It is suggested that those nanostructures could come from the thermal expansion and lattice mismatching between Si substrate and La_Sr_Cu_O thin film.If the growth of the nanostructure can be controlled,it could be used to form high_Tc junctions by directly growing.