According to the principle of improving the light output from scintillators by using photonic crystals (PhCs), we add four PhCs to the 5-μm-thick surface of a lutetium-yttrium oxyorthosilicate (LYSO) scintillator to improve the performance of the scintillator detectors. Four PhC structures are used, i.e., hexagonal air-holes, square air-holes, square cylinders, and square cubic rods. By scanning the period, ratio, and height of PhCs, we acquire four optimized structures using the Rsoft and MATLAB softwares, which is performed under the condition of a 420-nm-center wavelength of LYSO. The simulation results indicate that all the optimized PhC structures exhibit an increased light output and the structure with hexagonal air-holes shows the highest output (up to 17.1945%).