China Fusion Engineering Testing Reactor (CFETR) is a superconducting magnet tokamak. The research and development of the key technologies to the vacuum vessel (VV) manufacture have been carried out a few years ago by the Institute of Plasma Physics, Chinese Academy of Science, Hefei, China, including narrow-gap welding, cutting, and nondestructive testing. The manufacture of the poloidal segment (PS) for first 1/32 sector VV mock-up has been completed in 2015; the four PS sectors have been welded into a whole in 2016. This paper will describe the study of the welding process of the 1/32 VV mock-up for CFETR.