Like pinch-and-swell structure, Fish-head boudin is another kind of structure resulting from the difference between layer and matrix taking advantage of pure shear mechanism. On the basis of the research on shape of fish-head boudin and the difference between layer and matrix, and by means of the method of physical modeling, the author modeled different shapes of fish-head boudin, and came out the relationship between shape of fish-head boudin and viscosity ratio between layer and matrix, which can be called an experience rheological gauge. Taking account of the characteristics of pure shear and plane strain, after the measurement to fish-head bodins' present shapes and the resume of their original shapes, with several reasonable and ideal presumes, the author put forward the refraction rheology gauge of fish-head boudin.