Abstract: The varying-coefficient single-index models (VCSIM) have been applied in many fields since they combine the advantages of single-index models and varying-coefficient models. In this paper, their estimation method is proposed based on B-spline approximation technique and two calculation methods can be used. The first one is to directly calculate the parametric and nonparametric parts simultaneously by Newton-Raphson iteration algorithm. The second one is to calculate the two parts by profile method individually. We suggest that the second method is for our preference when the large amount of parameters are involved, otherwise the first method will be more convenient. Two simulated examples are given to illustrate the performances of the proposed estimation methodologies and calculation procedures.