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Schlieren technology can realize the visualization of flow field testing. The transmission schlieren device as a model, a laser light source with Gaussian distribution is used to pass through a cylindrical area with uniform refractive index distribution to obtain a simulated schlieren image and a flow field visualized diffraction fringe. Based on the theory of Fourier optics and applying Fresnel diffraction optics technology, the Fourier characteristics of the lens are derived, and the light field distribution at the focal plane of the lens is calculated. The Heaviside step function is combined to express the light field distribution on the back surface of the knife-edge device, and then the light field intensity expression of the imaging plane is obtained. The results show that the transmission schlieren method can obtain a high imaging quality light field intensity distribution map containing the parameters of the test object. When the cutting position of the knife edge is half of the light field spectrum surface, the imaging plane display effect is the best. In the comparative experiment, when the knife-edge device cuts the spectrum surface 2/5~1/2, the test object parameter information contained in the light field intensity map is the most complete. The intensity of the part that is shielded by the knife edge device is 0, and the intensity of the unshielded part is constant, which is consistent with the performance result of ray optics. This algorithm can provide theoretical basis and experimental reference for the visualization of typical flow field.
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