The traditional measurement of features on ship sub-assembly often uses manual measurement, which greatly relies on the measurement methods of measurement personnel and is not convenient for data recording. This low precision and low efficiency measurement method does not conform to the concept of digital shipbuilding.This paper introduces a visual measurement system comprising an embedded line laser sensor and a ship sub-assembly welding robot. When measuring features, as the welding robot moves, the sensor is brought over the feature to be measured, scans it, and calculates the feature's dimensions. This system is suitable for measuring various types of features in ship sub-assembly workpieces and does not require specific positioning of the workpiece. To validate the feasibility and accuracy of this system, we focused on circular groove hole features in ship sub-assembly. Measurements were conducted both in a laboratory setting using small-sized standard components and in a shipyard's real-world workpiece environment. Experimental results showed that when measuring standard components, the size error was less than 0.05mm, with a repeatability accuracy exceeding 0.02mm. In on-site measurements, the repeatability accuracy for length and width measurements was 2mm, and the positional measurement accuracy was 3mm. This measurement system can meet the precision requirements of shipyard manufacturing operations while reducing manual intervention and enhancing inspection efficiency.