Aiming at implementing the digital pulse interval modulation (DPIM) for optical wireless communications (OWC), a dualmapping technique is presented. The scheme of DPIM train based upon the dual-mapping technique is given. Its slot error rate is derived for the avalanche photonic diode (APD) receiver model, and is compared with that of classical DPIM.Simulation results show that the dual-mapping DPIM (D-DPIM), which has a fixed slot length, only has marginally inferior error performance, but can solve waiting slots or buffer overflowing in comparison with DPIM. Hence, it is suitable for the optical wireless communication systems.