Magnetic technology can significantly change the characteristics of crude oil, and the physical mechanism has received much attention for several years. To date, there is not yet an accurate conclusion. Terahertz time-domain spectroscopy is employed in this paper to characterize the optical parameters of selected wax-bearing crude oil under the action of a magnetic field. The corresponding absorption coefficient and extinction coefficient of samples are obtained by a fast Fourier transform frequency domain spectrum, and the aggregation characteristics of particles are analyzed in crude oil under a magnetic field. The decrease of the extinction coefficient may be suggested as qualitative proof of a magnetic-field-induced disaggregation of the suspended colloidal particles. Terahertz time-domain spectroscopy may be a powerful tool to characterize the particle disaggregation state in crude oil.