The article considers the features of computer simulation of diffraction and interference phenomena. Mathcad is ideal for modeling and visualizing various optical phenomena. These phenomena include slit diffraction. The phenomenon of diffraction is well studied, and the formulas describing it are given in the optics section of the physics literature. Using these formulas, a visual diffraction model for a two-dimensional situation was first constructed. On the basis of this model, a graph was constructed, which clearly shows the change in light intensity in the cross section of the hole. The level of visualization of the diffraction phenomenon is increased to a three-dimensional situation and presented graphically. According to the accepted assumptions, the curve of the intensity of light described in a plane coincides on any section of the surface in space, and the intensity of light is characterized by the height of the surface. In other words, the light intensity is constant along the length of the hole section, boundary effects in the section are not taken into account in the accepted model. When we observe light coming out of a small hole, we see interference rings called Newton's rings. It is easy to see that the intensity of light is maximum in the middle of the ring, and it seems to oscillate as it moves away from it.