The booster provides electron and positron beams to the CEPC collider for top-up injection at different energy.An 10 GeV linac is adopted as the injector. Then the beam energy is accelerated to specific energy according to three modes of CEPC collider ring (H, W and Z). The booster is in the same tunnel as the collider, placed above the collider ring and has exactly same survey as the collider ring except for the interaction region. Bypasses are arranged to avoid the detectors at IP1 and IP3 from the outer side. The optics/geometry design,injection/extraction scheme and DA study was shown in this paper.