The invention provides a method for determining the three-dimensional microstructure of asphalt based on a small-angle neutron scattering technology, which belongs to the technical field of asphalt microstructure determination methods. The method provided by the invention comprises the steps that firstly, an asphalt sample with the diameter of 25 mm and the thickness of 1 mm is prepared by using arheometer and two quartz plates or sapphire sheets; then the asphalt sample is tested by a small-angle neutron scattering spectrometer to acquire an absolute scattering intensity curve; and finally,an asphalt microstructure model is selected according to the intensity curve and the material structure form, and the characteristic parameters of the three-dimensional microstructure of asphalt are calculated. According to the invention, the three-dimensional microstructure of the asphalt material can be accurately characterized to the nanometer level; structural parameters such as asphaltene diameter, colloidal thickness and fractal dimension are calculated, which is helpful for understanding the microstructure components of asphalt and provides a theoretical basis for explaining the macroscopic rheological properties of asphalt; and the method is of great significance for the modification, evaluation, design and alternative material development of asphalt.