The pre-assembly of ITER bottom correction coils (BCCs) is a key milestone of large magnet coil assembly after PF6 / PF5 coil pre-assembly in ITER Pit on site. Because the BCCs should be installed between PF6 and the feeder rings, the assembly positioning of BCCs becomes a difficult construction with the narrow assembly gaps, the specific shape, and a high accuracy requirement of assembly. Therefore, the visual assembling technique based on alignment and measurement data was developed. According to the position measurement data of the positioned parts, the distribution of data, and the condition of sight lines in ITER Pit, using the delivered measurement data of BCC profile, the visual analysis, the position adjustment of the coils, and supports are performed, the lifting paths are optimized, the measurement process during lifting is simulated, and the assembly gaps are planed reasonably, to ensure the lifting safety and the positioning accuracy of the coils. The pre-assembly of six BCCs was successfully completed, the feasibility of the visual assembly technology based on measurement data was verified.