Along with the CAD technology being popularized, three-dimensional design of aircraft is ultimately realized into digital design. However, aircraft tolerances have not been designed by computer. They are mainly based on lots of manual calculations and not coordinated with integrated design and hold back the development of aircraft digital design and manufacture technologies. This paper introduces how to develop computer-aided aircraft tolerance analysis and distribution modules on UG and introduces Monte Carlo tolerance analysis technology. Running instances of aircraft tolerance design are illustrated in the paper.