The invention discloses a method for measuring the sag of advanced TFT substrate glass. The method comprises the following steps: S1, preparing a TFT substrate glass sample to be measured; s2, pastinga shading strip along the center line of the bottom surface of the TFT substrate glass sample; s3, placing the TFT substrate glass sample on a test bracket; s4, placing a laser range finder on the test platform, measuring the vertical distance Hmin from the test platform to the lowest point of the TFT substrate glass sample by using the laser range finder, wherein the sag of the TFT substrate glass is equal to H0-Hmin-H1, H0 in the formula is the height of the test bracket, and H1 is the thickness of the shading strip; using the laser range finder for measuring the glass sag, wherein the measuring mechanism does not contact with the glass surface to avoid shaking interference on the test result caused by contact between the measuring mechanism and the glass in the measurement process; thelaser range finder can move on the test platform, and the data of the center of the glass can also be measured, thereby ensuring the accuracy of measurement.