In order to improve the transmission performance of visible light communication link, a hybrid modulation system of carrier free amplitude phase(CAP) and amplitude differential pulse position modulation(ADPPM) is proposed. The system combines spectrum efficient multidimensional CAP modulation with power efficient ADPPM, and uses the time slot pulse of ADPPM to carry the CAP signal for information transmission. Under the Gaussian white noise channel model, the analytical expression of frame error rate of CAP-ADPPM hybrid modulation system is derived and verified by simulation. The influence of the order and amplitude of the hybrid modulation system on the frame error performance of the system is analyzed. The experimental results show that when the spectral efficiency is the same, the reliability of CAP-ADPPM hybrid modulation system is better than that of traditional single modulation system, and can provide a variety of parameter selection schemes, which provides a more flexible design choice for visible light communication.