NURBS surface is very useful in geometric modeling, animation, image morphing and deformation. Constructing non-self-intersecting (injective) NURBS surfaces is an important process in surface and solid modeling. In this paper, the injective conditions of tensor product NURBS surface is studied, based on the geometric positions of control points, which is equivalent to the surface to be non-self-intersecting for all positive weights. Finally, some representative examples are provided.