In order to improve the transmission performance of indoor visible light communication system, a hybrid scheme of carrierless amplitude and phase(CAP)-digital pulse interval modulation(DPIM) based on generalized spatial modulation(GSM) is proposed. Based on the joint idea of space-time, CAP signals are loaded onto DPIM slot pulses in signal domain to construct mixed modulation signals, and multiple antennas are activated simultaneously through GSM technology in optical domain for information transmission. The theoretical expression of the frame error rate of the GSM-CAP-DPIM hybrid system in visible Gaussian channel is derived. The accuracy of the analytical expression is verified by simulation, and the influence of different space time parameter selection on the system frame error performance is explored. The experimental results show that the reliability of GSM-CAP-DPIM hybrid system is better than that of traditional hybrid modulation system with the same spectral efficiency.