LaAlO3 thin films were fabricated on p-Si (100) substrates by using radio-frequency magnetron sputtering deposition method at room temperature. Then the samples were annealed at 800 ℃,900 ℃ and 950 ℃,respectively. The structural,morphological and optical properties of LaAlO3 thin films annealed at different temperature were investigated separately by X-ray diffraction (XRD),atomic force microscopy (AFM) and fluorescence spectrophotometer. The results of XRD and AFM show that annealing at higher temperature can improve the crystalline quality of the films. The films changed gradually from amorphous to crystalline above 900 ℃. Two emission peaks located at 368 nm and 470 nm in photoluminescence (PL) spectra are observed,respectively. The intensities of PL peaks increased with increasing annealing temperature. According to the absorption spectra and the calculated defect energy levels of the LaAlO3 films,it can be proposed that the 368 nm UV emission originates from the defect energy level of oxygen vacancies to the top of valence band and the 470 nm blue emission is derived from electron transition between the energy level of negative electricity AlLa anti-site defects and the top of valence band.