In the paper, Laser Measurement System (LMS) is used to monitor region in ship lock of the Three Gorges Project. Several methods are carried out to detect objects in the region. First, in order to determine whether there are ships in detected region, a distance difference integral method is given. Second, in order to decrease the random noise affection, the neutralization and the relativity of the fore-and-aft data are used to eliminate the noise and to eliminate misjudge from the random data. Third, two LMSs are installed to trace the motive object, a fixed LMS detects a linear region, and the other LMS can be rotated to scan a plane region in ship lock. As the fix LMS detected some motive objects, the other LMS begins to rotate and trace changed region and to determine whether there are objects in detected region. Finally, Laser Measurement System is tested in SanBo ship lock in ZheJiang province of China. All the methods are very effective. And the system will be installed in permanent ship lock of the Three Gorges Project in 2003. The system will keep the safety of the lock.