The surface acoustic wave(SAW) frequency domain reader based on the frequency step continuous wave(FSCW) uses the principle similar to that of vector network analyzer(VNA) for measuring the frequency domain response to resolve the echo information of the SAW tag. Firstly, the theoretical derivation of frequency domain sampling principle based on FSCW is carried out to guide the design of the reader’s parameters. Then, by combining the direct digital synthesizer(DDS) and the IQ modulator with the built-in phase locked loop (PLL), a fast frequency-converting transmit chain is designed, and a bidirectional coupler and a hardware IQ demodulation chip are used in the receive chain to realize quadrature coherent mixing, which realizes the stable measurement of the absolute phase. Finally, the circuit board of the reader is actually made, and the performance of the reader is tested with the SAW tag. By comparing with the measured results of the VNA, it is showed that the reader designed in this paper is effective.