Abstract：Abstract：Investigation on negative skin friction(NSF) is complicated in the effort to connect with some other theoretical problems in soil mechanics field. Consequently，it could help to advance our understanding on these problems in soil mechanics field in the NSF. However，some theoretical problems of the NSF are not interpreted reasonably. In order to understand the problems three important theoretical problems of the NSF：the dominant influencing factors of the NSF，the relation between NSF，and weight of the soil mass around pile and the power sources of the NSF are analyzed. Based on the in-situ data and theoretical analysis，two dominating factors，i.e.，the effective weight of the soil mass above certain depth and the settlement of the soil mass around the pile at the certain depth，are discussed. Then on the basis of the two above-mentioned dominating factors，the NSF could be regarded as a force acted on pile due to the lost gravitational potential energy of the subsiding soil mass，and as the force limited by shear strength of the soil mass. Finally，a theoretical model of power sources of NSF to illuminate the results is established.
