In order to improve the performance of indoor Visible Light Communication(VLC) system, a hybrid modulation scheme combining Carrierless Amplitude Phase(CAP) modulation and Digital Pulse Interval Modulation (DPIM) is proposed. This scheme takes advantage of both characteristics of higher spectral efficiency and power efficiency. A parallel modulation structure is adopted to realize the signal generation at the transmitter side, and the transmission of Direct Current biased Optical-CAP(DCO-CAP) signal are controlled by pulse time slot of the pulse interval modulation. The threshold value detection and the maximum likelihood criterion are used to complete the serial demodulation of modulated signals at the receiver side. Analytical expressions of Bit Error Rate (BER) and Frame Error Rate (FER) for the hybrid modulation scheme over Gaussian channel are derived. In addition, the performance of the proposed scheme and ordinary schemes are contrastively analyzed in terms of spectral efficiency and system reliability. The numerical results show that the hybrid system is more reliable compared with ordinary modulation system under the condition of same spectral efficiency.