A new modulation scheme called dual pulse-pulse interval modulation (DP-PIM) is proposed for optical wireless communication systems by resolving the problems which exist in fixed-length digital pulse interval modulation (FDPIM),pulse position modulation (PPM),and digital pulse interval modulation (DPIM). Based on given symbol structure,bandwidth requirement,average transmission power and capacity are studied. Meanwhile,the packet error rate is derived based on weak turbulence channel model. After compared with on-off keying (OOK),PPM,DPIM and FDPIM,the theoretical and simulation results show that DP-PIM has no problem such as overflow and underflow in the buffer by fixing the symbol length. DP-PIM also has built-in symbol synchronization as same as DPIM and FDPIM,meanwhile offers higher bandwidth efficiency and transmission capacity by reducing the average symbol duration for the given parameters. Hence,DP-PIM is superior in optical wireless communication systems.