In order to improve the low power efficiency of DCO-OFDM system and reduce the high complexity caused by high-order signal modulation，subcarrier index-power modulated with superposition multiplexing（SIPM-SPM）is applied to asymmetrically clipped optical orthogonal frequency division multiplexing（ACO-OFDM）system. The proposed signal transmission technique adopts SPM to add two complex data encoded by 8PSK and QPSK for the high power subcarriers， which further increases the transmission capacity and avoids the power loss caused by DC bias in ACO-OFDM system. Simulation results that in ACO-OFDM system，compared with SIPM（8-PSK/QPSK），the signal transmission capacity of SIPM-SPM is increased by 28.6%. Compared with SIPM（32-PSK/QPSK）with the same signal transmission capacity， when the bit error rate is 1.0 × 10-3，the signal-to-noise ratio gain is > 2.8 dB，the dispersion tolerance is increased by > 560 ps/nm，and the optical launch power dynamic range is improved by > 6.7 dB. It is shown that the combination of SIPMSPM modulation and ACO-OFDM system improves the noise resistance performance，high dispersion tolerance and reduces the demand for optical launch power.