Considering the conventional multi-pulse position modulation (MPPM) in free atmosphere optical communication, a hybrid MPPM modulation scheme based on modified binary phase shift keying (BPSK) is proposed. In the scheme, BPSK-modulated optical pulses are transmitted in a BPSK-MPPM hybrid frame and as the transmitted information is carried by both position and phase of the transmitted pulse, the change of optical pulse position is used to transmit more bits. The modified system model, channel transmission characteristics, bandwidth utilization, transmission efficiency and channel capacity are researched and measured, which are also compared with those of traditional schemes. Simulation results show that bandwidth utilization and transmission efficiency of the proposed scheme are higher than those of the ordinary schemes. In addition, the channel capacity in the hybrid MPPM frame construction including protected slots is also higher than that of the ordinary schemes.