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In this paper, we propose a frequency expanded method based on non-interferometric phase retrieval which can retrieve complex multi-level phase image by using only 1 times Nyquist frequency. Our proposed method utilizes the property of frequency spectrum periodicity and is the unique method with non-interferometry due to the intensity detection directly on the Fourier domain. For a regular phase image, same spacial frequency means same spectrum width. We choose a rectangular window with the same spacial frequency to the phase image and consider normalized Fourier intensity distribution of the rectangular window as the envelope of that of the phase image. After normalizing the spectrum of the phase image, we can expand its Fourier frequency with 1 times Nyquist size to other higher order frequency positions. Therefore, we can generate high-order frequencies artificially from low-order frequency which help us to retrieve phase image accurately and quickly.