The invention relates to a method for measuring a liquid refractive rate based on the total reflection diaphragm effect, which comprises the following steps of: washing panel image display glass and panel transmitting glass; adding a drop of liquid to be measured on the upper surface of the panel transmitting glass; pressing the upward roughening surface and the downward optical surface of the panel image display glass on the liquid to be measured; leading the liquid to be measured to form a liquid film between the panel transmitting glass and the panel image display glass; vertically projecting and transmitting visible light into the panel transmitting glass by a light through hole and passing through the liquid film of the liquid to be measured to enter the panel image display glass; forming a circular dark spot adopting an incidence light spot as a circle center on the roughening surface of the panel image display glass in a dark chamber with the luminance of 0.5-2Lux; calculating a radius r by measuring the diameter of the circular dark spot and calculating the refractive rate of the liquid to be measured. The invention has less measurement data, measurement precision of +/-0.003, low requirement on measurement condition, less dosage of the liquid to be measured and display of measured optical images during light illumination without debugging and can measure the refractive rate of the liquid in real time.