Orthogonal frequency division multiplexing (OFDM) signal has a very high peak-to-average power ratio (PAPR), resulting in a serious decline in the performance of OFDM systems. Although original selective mapping (OSLM) can obviously reduce the PAPR of OFDM signals, it has large complexity. In order to reduce computational complexity, a low complexity SLM named threshold classification SLM (TC-SLM) has been proposed, which utilizes two orthogonal phase factor sets and threshold classification to reduce the complexity. Simulation results show that the proposed TC-SLM not only successfully achieves a reasonable PAPR performance, but also can reduce the computational complexity clearly.