The transport of intensity equation(TIE) offers an experimentally simple technique for computing phase information directly from several defocused images. In this work we developed the traditional TIE intensity acquisition system. In order to avoid the shifting of CCD, a quadratic phase pattern was displayed on the SLM to provide a lens effect for realizing different defocus distance by varying the focal length of the lens. Two kinds of phase imaging experimental configurations guided by two different theories were designed. In most instances, since a camera is used to capture images in which the phase modulation of lens cannot be ignored, the former intensity acquisition system was designed based on the single lens optical propagation system, and the relationship between the focal length and the image distance in the lens law was used to facilitate the varying of the defocus distance by changing the phase pattern displayed on the SLM. The latter was designed by locating a SLM in the Fourier domain of the 4f setup, according to the Fourier transform property of the lens and the Fresnel diffraction theory, the relationship between the defocus distance and the focal length of the quadratic phase pattern can be derived. The experimental results verify that the proposed phase retrieval methods are reasonable and correct.