The signal-to-noise ratio (SNR) of DBPM signal is one of the important parameters to measure the performance of BPM, and it plays a decisive role in the resolution of beam position measurement. Based on the position measurement resolution requirements of high energy photon source (HEPS) for BPM, this paper firstly introduces the overall architecture of BPM system and deduces the signal-to-noise ratio of signals at all levels in the signal link of BPM system. Then the calculation method of ADC sampling clock jitter and BPM electronics test platform are introduced. The conclusions in this paper can be used as a standard to judge whether each part of BPM system can meet the requirements of HEPS, which is of great significance to promote the batch application of self-developed BPM electronics in HEPS engineering.