The invention discloses a measurement method of a protected layer swelling deformation quantity. The method comprises the steps of (a) using a drilling machine to drill a hole, (b) using the drilling machine to carry out reaming operation on the drill hole, (c) sending a top plate displacement measuring device to the top of the drill hole, and then sending a bottom plate displacement measuring device to the top end of an expanded hole, (d) fixing a hollow rod to the opening of the drill hole, (e) recording top plate displacement measuring device initial data d1 and bottom plate displacement measuring device initial data d2, (e) after the protection layer working surface is pushed, reading top plate displacement measuring device initial data d3 and bottom plate displacement measuring device initial data d4, (g) substituting the data collected in two times into a formula D=(d4-d2)-(d3-d1) to calculate and obtain the protected layer swelling deformation quantity. According to the method, the displacement measuring devices are arranged at the top plate and the bottom plate of a protected layer, the factors of unstable drill hole and unstable collapse holes are overcome, the swelling deformation of the protected layer can be timely captured, and the measurement is more accurate.