The absorption characteristics of ytterbium-doped single-cladding fiber are studied experimentally. The effects of pump power, fiber length and seed power on the absorption characteristics are analyzed. The results indicate that, under the situation of absorption saturation, the fiber can resorb 40～60 mW pump power for every 100 mW increase of pump power, and the absorption coefficient tends to a constant with the increase of pump power. The re-absorption capacity and the absorption coefficient of the fiber can be improved with the increase of the fiber length. Besides, it is another way to significantly improve absorption ability of pump light that injecting seed light.