ZnO films were deposited on p-Si (100) substrate by pulsed laser deposition (PLD). Then the samples were annealed at 500 ℃, 600 ℃ and 700 ℃ respectively. X-ray diffraction (XRD) was employed to analyze the effects of annealing on the crystalline structure of the ZnO films. The sheet resistance of the ZnO films and the I-V characteristics of the heterojunctions were also studied. The results show that higher annealing temperature enhances the films' crystal quality. The intensity of the (002) diffraction peak increases and the full width at half maximum (FWHM) decreases with the rise of annealing temperature, mean while, the internal stress in film decreases and the ZnO crystal grain size increases. Without light illumination, the dark leakage current of the heterojunctions increases with the rise of annealing temperature. With illumination of 650 nm light, the best photoelectric effect is obtained from the sample annealed at 600 ℃. It is revealed that the interface of the heterojunctions might be degraded at higher annealing temperature. Therefore, proper annealing temperature is necessary for high quality photoelectric devices.