This paper analyzes the performance of reducing the peak-to-average power ratio (PAPR) by partial transmit sequences (PTS) in OFDM system, and finds that it is dependent on the correlation of several candidate signals which is decided by subblock partitions and phase factors, while it is unconcerned with the input signal. The authors also prove that random subblock partition is more favorable than interleaved and adjacent subblock partitions by analysis and simulation