In order to balance the peak-to-average power ratio (PAPR）and high complexity of coherent optical orthogonal fre-quency division multiplexing (CO-OFDM）, a novel joint algorithm based on active constellation extension-projection onto con-vex sets (ACE-POCS）and iterative partial transmission sequence (IPTS）is proposed, which is called the improved iterative par- tial transmission sequence of active constellation extension (ACE-IPTS）. The simulation results show that, compared with the o-riginal signal, the PAPR0 of ACE-IPTS algorithm is optimized by 4.907 dB. ＼hen the bit error rate is 10 -3, the optical sig-nal-to-noise ratios (OSNRs）of ACE-IPTS and improved ACE-POCS increase by 0.54 dB and 1.04 dB respectively compared with the IPTS algorithm. The calculation times of IPTS, ACE-IPTS and ACE-POCS are 59392, 79872 and 204800 respectively. Compared with ACE-POCS algorithm, the calculation times of the ACE-IPTS algorithm decreases by 61%.