Due to the transmission of transmitter the high peak-to-average power ratio (PAPR) and large spectrum side lobe power are two main drawbacks in non-contiguous orthogonal frequency division multiplexing (NC-OFDM) based on cognitive radio (CR) systems. In this method we proposed a new signal cancellation (SC) method for joint PAPR decrement and side lobe suppression in NC-OFDM based CR systems. The scheme for proposed method is to dynamically increase a part of constellation points on the secondary user (SU) subcarrier and add minimum signal cancellation symbols on the primary user (PU) subcarrier, for an accurate cancellation signal for joint PAPR reduction and side lobe suppression. The further process of the SC method formulates the difficulties of the joint PAPR reduction and sidelobe suppression as a quadratically constrained quadratic program (QCQP) to obtain its optimal cancellation signal. We also use the suboptimal SC (Sub-SC) method to effetely overcome the QCQP optimization problem with minimum computed difficulty and the final results show the SC method and Sub-SC method organize both characteristics of PAPR reduction and sidelobe suppression.