In current interior design, computer software CAD-3D is a commonly used design software that can provide more reference information for interior designers, thereby better improving the efficiency and quality of interior design. In practical applications, it is necessary to convert CAD and 3D software reasonably to better improve the conversion efficiency between CAD and 3D. In order to understand the conversion method of CAD-3D and fully utilize this function, this article will conduct relevant research, mainly introducing the basic concepts of CAD and 3D, and then discussing the CAD-3D conversion method and functional application mode, hoping to provide reference assistance. Through research, it has been found that CAD can meet people's needs for three-dimensional space by modifying two-dimensional graphics. 3D software is a type of 3D software that can be used to draw 3D models to better meet people's needs for 3D space. Due to the fact that both CAD and 3D are software used for design, it is necessary to convert them reasonably in practical applications.