To further improve the accuracy of phase measurement, the Shanghai Synchrotron Radiation Facility (SSRF) Beam Instrumentation (BI) Group proposed a new signal processing method, the correlation function method, based on the bunch-by-bunch phase measurement system. This method calculates the bunch-by-bunch phase by performing pattern matching directly on all sampling points of the oscilloscope in the time domain. The advantage is that the data processing is only limited by the oscilloscope bandwidth, and more BPM (Beam Position Monitor) harmonic signals can be retained. The results show that increasing the BPM signal processing bandwidth can effectively remove the crosstalk between bunches and reduce the system measurement error caused by signal reflection. The principal component analysis (PCA) method is used to evaluate the phase measurement resolution, the larger bunch charge, the better the resolution. The precise phase dependence between the bunches can also be used to analyze the beam wake field and impedance in the storage ring.