In this paper, a two-path parallel scheme for m-QAM-OFDM transmission in optical wireless communications was proposed, and its principle was theoretically derived. This scheme transmitted two-path parallel OFDM signals, which carried m-QAM mapped data symbols and their conjugated data symbols respectively. Simple superimposition at the receiver was performed to mitigate the inter-carrier interference (ICI). The feasibility of the scheme was experimentally demonstrated over a turbulent-air-water channel. The results show that the proposed scheme was not sensitive to time delay between the two paths, and it brought significant improvement of bit error rates (BER) performance compared to conventional single-path m-QAM-OFDM transmission scheme even in the turbulent-air-water channel. The proposed scheme has great potential in free space optical (FSO) communications, visible light communications (VLC) and underwater optical wireless communications (UOWC).