The invention discloses a method for testing grouting compactness of a pre-stressed duct. The method comprises the following steps: S1, calibration of testing lines: marking a grouting compactness testing line on a side face of a duct region on a beam column, and marking a grouting compact part testing line on a side face of a duct-free region on the beam column; S2, arrangement of testing points: arranging N testing points on the grouting compactness testing line and the grouting compact part testing line; S3, numerical value acquisition: acquiring the reflection wave velocity Vi of a certain testing point on the grouting compactness testing line and acquiring the reflection wave velocity Vsdi of the certain testing point on the grouting compact part testing line; S4, quantitative computing: judging whether the reflection wave velocity of the certain testing point on a certain grouting compactness testing line changes suddenly or not. The method can be used for quantitatively detecting the compactness of the pre-stressed duct.