Embodiments of the invention provide a noise barrier on-line measurement method and a system. The noise barrier on-line measurement method comprises the following steps: step 1, a laser vision sensor acquires the relative displacement of a noise barrier when a train moves; step 2, whether the relative displacement is greater than a displacement threshold is judged, and a judgment result is generated; step 3, when the relative displacement is greater than the displacement threshold, the judgment result shows that there is a risk that the noise barrier may be loosened; and step 4, the judgment result is output. With the method and the system of the invention, the looseness fault of a high-speed railway noise barrier can be detected intelligently, and the problem that manual patrol inspection is of low efficiency and affected by subjective factors is overcome.