The iterative partial transmit sequence (IPTS) clipping algorithm is used to reduce the peak- toaverage power ratio (PAPR) of 100- Gb/s high- speed polarization division multiplexing coherent optical orthogonal frequency division multiplexing (PDM- CO- OFDM) system. PAPR, bit error rate (BER), and nonlinearity performance are analyzed. Simulation results demonstrate that the PAPR, BER, and nonlinearity performance of IPTS clipping algorithm are superior to those of clipping algorithm. At the complementary cumulative distribution function (CCDF) of 0.0001, the threshold value of IPTS clipping algorithm is optimized by 0.62 dB compared with clipping algorithm. Compared with original signal, the maximum peak power of IPTS clipping algorithm is reduced by 2.63 dBm. In the same conditions, the needed optical signal to noise ratio (OSNR) of IPTS clipping algorithm is 12.28 dB to reach the BER level of 10- 3. However, the minimum BER of clipping algorithm is only 1.55× 10- 3. At the launch power of - 1 dBm, the Q value of IPTS clipping algorithm is improved by 0.28 dB compared with clipping algorithm.