The process of grid generation and flow field simulation can be automated to enhance the efficiency of CFD simulation, which has a great potential for applications. This paper proposes an auto-CFD technology framework based on the tie-dye algorithm, which can generate grids automatically and initiate inviscid flow field calculation quickly without geometry clean-up after inputting solid models. A 2D numerical example verifies that the calculation accuracy of this technology is comparable to that of the unstructured finite volume method, but with a significant improvement in calculation efficiency. Moreover, a 2D Auto-CFD software is developed that can start the calculation automatically with hand-drawn models in real time. The Auto-CFD technology is also extended from 2D to 3D space, and the irregular point cloud obtained by laser scanning the car is used as the solid model to demonstrate the adaptability of this technology to complex shape problems. This paper employs the tie-dye algorithm, which is compatible with all finite difference methods and has a strong universality. It is expected to overcome the technical difficulties in the existing Auto-CFD software.