Abstract: The digital stereo encoder applied in FM broadcast is accomplished with DSP chip TMS320C50 and high-speed A/D chip. The method of digital interpolator in digital FM stereo encoder is proposed. This paper also discusses the design of digital filter based on Kaise window in detail, which is used to increase the sampling rate. This method not only improves the acoustic quality and the isolation level among stereo channels, but reduces the computation. The measuring results are also given in this paper.