The assembly mode of composite case is hand crossed positioning method. It's low precision, poor repeatability, high level requirements for the operators and using the metal marking needle can cause surface damage of the composite shell. In order to change the status of hand crossed positioning, the method of NC equipment combined with the spraying equipment for the parts positioning was proposed. For making sure the accuracy of parts contour and position, equidistant spraying was researched. NC positioning trajectory equating was built. Through connecting spraying equipment with CNC system to build up NC positioning system for parts. The contour and position of parts on composite case was marked. The positioning accuracy of parts can reach ±0.1mm, NC positioning replacing handicraft method was realized. The technology improves the positioning accuracy and consistency of parts in composite case.