A phase-only encoding method based on one-dimensional grating function is proposed. Based on double-phase hologram encoding technique, the complex amplitude image is encoded into a phase-only image, and then the image is directly loaded into the spatial light modulator for image reconstruction. During the optical reconstruction, a 4-f system with a low pass filter is used to select the diffraction order, and the first order diffraction component is chosen for reconstruction. The one-dimensional grating encoding function can improve the energy of the first order diffraction component. The quality of the reconstructed images is increased because there is no interference from zero-order information of the phase element. The numerical and experimental results show that the encoded amplitude and phase of the complex object can be reconstructed effectively, and the power of the first order diffraction got from the proposed method is higher than that of two-dimensional checkboard encoding function.