In order to solve some problems of static parameter detecting & measuring system for gun tube, we invented the engine common flat that adapted to different gun tube with measuring accuracy above 0.05% of axes orientation and above 0.1° of circle orientation. We designed the hardware common flat controlled by double MCU and the software common flat under the guidance of modular design. Three common flats connected with the flaw-detecting module which could detect all parameters of flaw to make the measuring accuracy of flaw’s length and depth above 0.1 mm. Three common flats connected with the measuring module of bore size to make the measuring accuracy of all parameter of bore size above 0.000 2 mm. The common flats also can connect with other measuring module to get other parameters of the gun tube.