In recent years, the interferometric imaging method has been applied to analyze the structure of various specimens, such as crystals and biological tissues. However, the interferometric imaging method may require a relatively complex optical recording system, such as a reference wave and temporal coherence. In this paper, we propose a method based on noninterferometric imaging for quantitative phase retrieval of complex-valued specimens. A strategy using different focal lengths in the lens function is developed, and a series of diffraction intensity maps is recorded. Numerical simulation results are presented to demonstrate the feasibility and effectiveness of the proposed method.