This paper proposes a hierarchical implicit surface representation which has good adaptability and is very suitable for representing level of detail models. The definition of hierarchical implicit tensor-product B-Spline surface (HITBS) is first given and a mathematical model for surface reconstruction is briefly reviewed. Then an optimization model is proposed based on HITBS and a method is introduced for decomposing the domain in an adaptive fashion. A hierarchical approximation algorithm is proposed to deduce a series of linear equation System. The partition of unity method is introduced to integrate the local approximate functions into a global one. Some examples are given and conclusion remarks are concluded.