The length of the manifold made of composite plate in the natural gas pretreatment plant is too long,and it needs to be transported to foreign countries for a long distance. In order to ensure the overall manufacturing quality and reduce the possible problems on site,the production scheme of overall fabrication in the plant,segmented cutting after pressure test,and final segment opening welding on site are adopted. The manifold has small diameter,thick wall and large deformation rate,according to its design material Q345R（R-HIC） + S31603 and structural characteristics,the manufacturing process and welding quality assurance measures of small diameter composite equ-ipment are introduced from the aspects of cylinder rolling,processing and welding. It has certain reference significance to the manufacture of the same type of equipment.