Abstract: Generally, the collimation correction must be made on almost all the measured data of small-angle X-ray scatterings. This requires to first employ either theoretical calculation or experimental determination in obtaining the weighting unctions of the instrument. Due to conceptional confusions, contradictions and fproblems are found to exist in methods of determination of the weighting functions suggested in the current literature.In accordance with the basic theory of collimation correction, the physical meaning of the weighting functions and the method of determination are expounded and discussed. As a practical example, a determination of the weighting functions of different small-angle scattering instruments has been made.