In this paper, a MIMO image sensors based visible light communication system is designed and researched. In our study, the spatial inter-symbol interference was considered and the formation mechanism of the stray light and the influence of the spatial inter-symbol interference is analyzed. The mathematics expression of the system SNR and BER is given. The simulation result indicates that there is a critical communication distance in the system. Once the communication distance exceeds the critical value, the system BER increases sharply. In addition, an adaptive threshold detection method is introduced and the performance is simulated. By means of estimating the spatial inter-symbol interference noise power, the optimal detection threshold can be obtained and the system BER performance enhances significantly.