Abstract: The signal processing algorithm is one of the keys for digital beam position monitor(BPM) system. In order to optimize the digital BPM algorithm effectively, it is important and significant to research the BPM algorithm offline by using MATLAB. In this paper, the principle and framework of digital BPM algorithm are introduced firstly, the raw ADC data is subsequently obtained from BEPC Ⅱ based on the digital BPM hardware platform, which is domestically made by Institute of High Energy Physics, Chinese Academy of Sciences. Then NCO module, CIC filter, FIR filter and TBT position data calculation modules are designed with MATLAB, and the specific design parameters of each module are provided. Finally, each algorithm module is tested using raw ADC data and signal spectrograms are given. The turn-by-turn position resolution in horizontal and vertical directions under the actual beam are 4.55 μm and 4.28 μm. The offline research provides a reliable theoretical basis for the implementation and optimization of FPGA algorithm.