Samples of amorphous-InSb/ZnS-SiO2 structure are deposited on K9 glass substrate with magnetron sputtering method in this study. Optical constants of amorphous InSb thin films are measured by a spectroscopic ellipsometer. The optical band gap is determined to be 0.26 eV by Fourier transform infrared spectroscopy. The nonlinear absorption and nonlinear refraction of the amorphous InSb thin films are measured through well-established Z-scan method at the wavelength of 405 nm. Results show that the amorphous InSb thin films show the characteristics of saturable absorption and self-focusing, the nonlinear absorption coefficient is -3.73×10-2 m/W, and the nonlinear refractive index is 6.64×10-9 m2/W. Based on the nonlinear absorption coefficient, the nonlinear absorption cross section is calculated, which is very close to the reported value of related literature. The thermo-optical effect is investigated by variable temperature ellipsometry method at the wavelength of 405 nm. Analysis indicates that the nonlinear saturable absorption mainly stems from nanosecond laser-induced thermal effect, whereas the self-focusing refraction mainly results from electronic nonlinearity, respectively. The super-resolution effect induced by the saturable absorption characteristic is simulated, and the results show that the nonlinear absorption effect of the amorphous InSb thin films can effectively reduce the size of the transmission spot.