Recent implementation of environmental geophysical exploration technique in rapid detection and evaluation of soil contamination is widely involved. Typical soil contaminants tend to alter the pore fluid and hence the variation of soil electrical properties, the transmission path of electrical currents or electromagnetic waves may be affected within the contaminated region. This in turn provided the detection basis of the electrical and electromagnetism geophysical methods. As contaminated soils consisted of composite materials of three or four phases, the relationship between their electrical properties and water content, porosity, contaminant concentration are relatively complex. The demand for a wide electrical spectral range has hence arisen for contaminated soil characterization. This study proposed an innovative time domain reflectometry (TDR) approach, in order to measure a broadband complex dielectric spectrum (including both real and imaginary parts of complex dielectric permittivity, CDP) within MHz–GHz frequency range and to perform a more complete electrical characterization of contaminated soil. The robustness, in-situ applicability, and performance of the proposed method is verified using series of laboratorial and in-situ experiments, involving various contaminants. The measurement system can be setup, calibrated, and operated easily, holding great potential for better hydrophysical and environmental characterization of soils.