Based on the model of wireless optical communication system channel under weak atmospheric turbulence, theoretically deduction and comparatively analysis are done on modulation symbol structure, transmission power, bandwidth requirement and packet error rate of the five digital modulation schemes (OOK, PPM, DPPM, DPIM and DH-PIM). The results show that PPM need both symbol and slot synchronization, while DPIM, DPPM and DH-PIM just need slot synchronization. OOK offers the biggest average transmission power, while PPM offers the smallest transmission power, the average transmission power of DH-PIM is smaller than that of OOK, while bigger than that of DPIM and DPPM. And the transmission power characteristic of DPIM is slightly smaller than that of DPPM. When M=6, comparing to average transmission power of OOK modulation scheme, PPM can save about 15 dB, DPPM and DPIM can save 12 dB, DH-DPIM can save about 10 dB with α=2. OOK offers the smallest bandwidth requirement, while PPM offers the biggest bandwidth requirement, the bandwidth requirement of DPIM is slightly bigger than that of DPPM. And the bandwidth requirement of DH-PIM is bigger than that of OOK, while smaller than that of DPPM. When M=6, the bandwidth requirement of PPM modulation is eleven times of that of OOK, and that of DPPM and DPIM is six times of OOK, that of DH-DPIM with α=2 is three times of OOK. Under the condition of the same mean number of absorbed background photons and the same mean number of absorbed signal photons per pulse, the packet error rates increase in order of PPM, DPIM, DPPM, DH-PIM and OOK.