The invention discloses a quantitative method and a quantitative device. The quantitative method includes the steps of: 1) when a medium is subjected to vibrating excitation, acquiring a position-time map that the vibration is transmitted in the medium; 2) by means of image segmentation, acquiring the slope of a slope line of the position-time map; 3) according to the slope, calculating the viscoelasticity parameter of the medium, wherein the slope of the position-time map represents the transmission speed of the vibration in the medium. Because the transmission speed of the vibration in the medium is relative to the viscoelasticity of the medium, the iscoelasticity parameter of the medium can be quantitatively calculated after the slope of the position-time map is acquired. The method is free of calculation of the slope of the position-time map by selecting a character point from the position-time map, so that the method is free of noise interference and is low in calculation load, and can high-effectively and accurately perform quantitative calculation of the viscoelasticity of the medium.