Faraday anomalous dispersion optical filter (FADOF) is a precision spectrometer with high spectral resolution and spectral stability. This article analyzes the method using dual-peak-transmission FADOF for solar Doppler observation, which develops FADOF transmission spectrum calculating software, and carries out the prototype experiment of sodium atoms FADOF with bimodal type transmission spectrum. Experiment shows good agreement between experimental results and theoretical ones, and the parameters meet the requirement of solar Doppler observation.