Abstract: The density of grouting in the prestressed ducts of rail transit bridges can affect the bearing capacity and durability of the structure. Therefore, nondestructive testing of the density of grouting in prestressed cable ducts has become the key to the safe operation of the structure. The authors theoretically analyzed the principle and method of stress wave detection of grouting compactness in prestressed ducts of bridges, conducted impact echo detection tests on experimental beams, and conducted tests in combination with practical engineering. The experimental results indicated that the proposed method can detect the grouting density of bridge prestressed cable ducts, and the results verified by the borehole endoscope method were consistent with the test results. This method had good applicability.