This paper describes a study on the application of smart mechanoluminescence (ML) sensor to structures for the visualization of stress distribution. Smart thin film sensor of ML material SrAl2O4:Eu/polyme is coated on the surface of structure. The sensor will emit visual light when the structure is subjected to deformation. The light intensity is proportional to the strain energy density and the equivalent strain of the stressed material based on the energy viewpoint and experimental facts. The distribution of visual light intensity is recorded using CCD camera or ordinary camera. Then the stress distribution can be evaluated from the distribution of visual light intensity based on solid mechanics and the relationship between light intensity and equivalent strain. Compression test of a disk with coated SrAl2O4:Eu/epoxy film sensor is conducted to compare the visual light distribution with the stress distribution obtained from finite element analysis. Furthermore, tensile test of a rectangular specimen with a coated SrAl2O4:Eu/polymer film sensor is performed to demonstrate the relationship between visual light intensity and strain. Experimental and numerical results show that the smart sensor of ML material SrAl2O4:Eu/polymer is an effective strain sensor to directly visualize the stress distribution in real time.