Abstract: For large-scale ocean engineering modules, the construction method is usually pre-fabricating in pieces and field-assembling on site. About the dimensional control, there are more control points for the structure and stricter tolerance for attached pipe docking because of the complicated structure and huge overall size. Taking Ichthys liquefied natural gas (LNG) land terminal project which was built on COOEC Qingdao yard as an example, dimensional control is applied to structure pieces and the best-fit center line is marked on them in the pre-fabrication process. Three-dimensional coordinate system control network is established on the final assembly site. According to the system, the positioning and dimensional control of structure pieces, as well as those of the pipe docking, are achieved using the best-fit center line. The three-dimensional coordinate system can effectively ensure the accuracy of the module in the field-assembly process and control the error accumulation, which provides experiences for the dimensional control of large-scale modules in the future.