FDM(orthogonal frequency division multi O-plexing) has become a popular technique owing to the the high spectrum efficiency and channel robustness. However, one of the serious drawbacks of the OFDM signals is the high PAPR(peak to average power ratio) which causes the nonlinear distortion and the power penalty at the transmitter. In this paper, a new SPW(subblock phase weighting) method is studied for PAPR reduction. Unlike the conventional PTS(partial transmit sequences) and SLM(selected mapping) method, PAPR is reduced by using only one IFFT block in the SPW method. Also, the insertion methods on the side information about the subblock phase control weighting to reduce PAPR are proposed for the correct demodulation of OFDM symbols. Compared with the conventional methods, the proposed SPW scheme quitely reduces the computational complexity PAPR by using. the adaptive PAPR threshold method. A new SPW method is basically examined. CCDF(complementary cumulative distributed function) of PAPR is evaluated in the cases that both feedback and feedforward type of the side information insertion are devised into the basic SPW method. PAPR reduction efficiency grows up as the number of subblocks is increased. However, there is a slight loss of the spectral efficiency due to the side information insertion. Feasibility of the proposed method and the validity of side information insertion method are proved and compared by the extensive computer simulations in terms of PAPR and computational complexity reduction. Therefore, the proposed SPW method can be applied into multicarrier system like OFDM as more effective PAPR reduction method.