Faster-than-Nyquist (FTN) technology can improve the spectral efficiency of Optical Wireless Communications (OWC). However, it is affected by the artificially introduced Inter-Symbol Interference (ISI) and atmospheric turbulence, which leads to the degradation of Bit Error Rate (BER) performance. To deal with this issue, a PAM modulated Multiple Input Multiple Output (MIMO)-FTN-OWC system is proposed, and MIMO technology is utilized to suppress the influence of atmospheric turbulence. Furthermore, the theoretical BER in log-normal fading channel is deduced, and the influence of channel correlation on the BER performance is analyzed. The simulation results show that the BER performance of 2×2 MIMO-FTN system is 9.5 dB higher than that of Single-Input Single-Output (SISO)-FTN system when BER is 10^-4. In addition, the MIMO-FTN system has better BER performance than that of SISO-FTN system when the channel spatial correlation coefficient is lower than 0.6.