Optical orthogonal frequency division multiplexing (O-OFDM) is an efficient modulation technology for reduction of intersymbol interference. There is a strict requirement for the linear characteristics of amplifiers in transmitters and receivers if the peak to average power ratio (PAPR) is high in the implementation of O-OFDM modulation technology, which limits the practical employment of O-OFDM. Various techniques on reducing the PAPR are summarized, and the definition and distribution of PAPR are introduced. In order to contain the PAPR in O-OFDM systems, a new scheme for optical OFDM system PAPR reduction using dummy subcarrier is presented, which does not need to send sideband information in the transmitter and does not need additional treatment in the receiver. The experimental results show that the method can not only reduce the PAPR and the complexity of the calculation, but also improve the bit error rate (BER) of the system when the O-OFDM signals transmits over 200 km standard single-mode fiber (SSMF).