  The upgrade project of Hefei Light Source storage ring is under way. In this
paper, the wake fields of new designed vacuum chambers have been simulated by
CST code, and then broadband impedances were obtained by FFT. Together with
resistive wall wake fields, broadband impedance model for storage ring was
established. Using theoretical formula, longitudinal and transverse single
bunch instabilities were discussed. With carefully-designed vacuum chamber, the
threshold of beam instabilities was higher than beam current goal.
