In order to improve the homogeneity of lightweight concrete and enhance the mechanical properties of lightweight concrete, the Herschel-Bulkley (H-B) plastic viscosity calculation model was established to explore the influences of rheological characteristics of foamed slurry on the foam settlement and ceramsite distribution in slurry. The results show that with the increase of thickener content, the yield stress and the plastic viscosity of lightweight concrete foamed slurry based on nonlinear H-B model ηH-B=0.016 67K(80n-20n) (ηH-B is the plastic viscosity of foamed slurry obtained by H-B calculation model; K is consistency coefficient; n is flow index) increase. As a result, the settlement distance of foamed slurry decreases and the fractal dimension of ceramsite in slurry increases. When the plastic viscosity of foamed slurry is greater than 1.74 Pa·s and the yield stress is greater than 92.87 Pa, the lightweight concrete with compressive strength greater than 10 MPa is prepared. It is seen that optimizing the rheological properties of the foamed slurry is the key to overcome the easy floating problem of ceramsite in foamed slurry, which can effectively improve the homogeneity of lightweight concrete and enhance the mechanical properties of lightweight concrete.