According to the principle of reflection of electromagnetic waves, the authors use the open-ended coaxial probe method which operate the high frequency electromagnetic wave (200 MHz-8.5 GHz) to measure the dielectric constant of sand saturated with water and LNAPL (light non-aqueous phase liquid) under the laboratory conditions. The experimental results show the real part of the complex permittivity increases with LNAPL volume increasing and the imaginary part changes very little. However, the variation of the complex permittivity is not obvious after the sand is saturated. When the quartz sand contains water, the real and the imaginary parts of the complex permittivity increase with the volumetric content of LNAPL increasing. After some hours, both the real and imaginary parts of complex permittivity of the sand partly saturated with water and LNAPL have changed. In the study frequency range, the real part of complex permittivity decreases gradually with the frequency of electromagnetic wave elevation, the changes of the imaginary part is different. The experimental results show that the change of the mixture structure due to the LNAPL replacing the air in the pore and the absorption of the LNAPL, water and medium changes the ionic polarizability and further changes the dielectric properties of the mixture.