Background: In order to improve the synchrotron performance in the constant current mode

attentions should be paid to problems such as non-linear beam dynamics

broadband beam impedance

and position disturbance

etc. Purpose: To address these problems

a bunch by bunch data acquisition system(BBDAQ) is implemented for real-time bunch position monitoring

as well as the off-line data analysis for the Shanghai Synchrotron Radiation Facility(SSRF) storage ring. It can be applied to optimize new equipment impedance

filling pattern

injection mode

and raise threshold value of current instability. Methods: This BBDAQ developed at SSRF consists a RF front end to filter and expand bunch signal to 2 ns

a data acquisition and processing card to sample bunch signal with four 125-MHz ADCs

which make an equivalent 500-MHz sampling rate

and the EPICS for post-processing to give bunch position and tune value. Results: Online experimental results show that the system can measure bunch by bunch position and tune value successfully. Conclusion: The development of bunch by bunch data acquisition system provides an efficient tool to analyze beam impedance

coupling instability

nonlinear dynamics. It makes further improvement of synchrotron performance visible.