In this paper, the method for measuring the complex permittivity of concrete has been proposed, and using this method the complex permittivity of concrete is measured. This method for calculating the dielectric constant of concrete is used by measuring the deflection and the loss of electromagnetic wave in concrete block for experiments. The measuring device used is a single frequency radar. Measurement process is divided into three steps: measuring attenuation factor alpha of concrete, measuring the refractive index of concrete and calculating the complex permittivity of concrete. The method is simple and feasible in practice.