  Both horizontal and vertical coherent beam-beam instability are important
issues at CEPC. The horizontal instability (X-Z instability) could be induced
by beam-beam itself. In this paper we try to study the effect of chromaticity
and resistive feedback by analysis and simulation. The vertical instability may
be induced due to the combined effect of beam-beam interaction and vacuum
impedance. Finite chromaticity and asymmetrical tunes have been proposed to
suppress the vertical instability. Due to the further increase of impedance
budget, we need to find more measures to mitigate the instability. The effect
of resistive feedback and hourglass effect are evaluated by simulation.
