Abstract: Streak camera was used to measure the longitudinal distribution of single bunch in Hefei Light Source. The result was used to research and verify the changes of longitudinal distribution of single bunch. The theoretical analysis was made for the effect of the potential well impacting on the bunch longitudinal distribution. The simulation results were given for the effect of the inductive impedance and resistive impedance impacting on the bunch distribution. Some experiments were made, for example, on the bunch length lengthening, and potential well distortions. The measurement mode was discussed about the potential well distortion of the bunch. The broadband coupled impedance of low frequency of storage ring is about 4.4 Ω by comparing the measured bunch length dependence on the current and comparing it to simulations in HLS.