Abstract: The digital transverse feedback system is used to suppress the transverse beam instabilities at Hefei Light Source (HLS). During the commissioning of the feedback system, a turn-by-turn measurement system has been adopted to gather beam position information for the assessment of its feedback efficiency. The growth and damping of beam instability were observed by gradually changing the chromaticity through varying the sextupole magnet current. Corresponding growth time and damping time of instability oscillation were calculated to be 0.258 ms and 1.172 ms, respectively. Beam characteristic parameters, such as tune and phase spaces, were measured and calculated. Moreover, the whole process of beam moving near and across the 5/9 resonant line was analyzed.