There is a fluctuation of symbols which results in error performance degradation if some errors occur in digital pulse interval modulation (DPIM) train. To address this issue, we present a novel demodulation scheme for DPIM. The decoding method is firstly proposed, and then the packet error rate is derived and compared with decoding using the optimal threshold method. Numerical simulation shows that the proposed method saves approximately 1.5 dBm average signal power than that of threshold method with different modulation levels when the packet error rate is 10-6 and information of packet n is 24 bit, but the improvement of error performance will degrade with the increase of n. Requiring no redundant information bits, the proposed method can effectively improve the error performance for DPIM, and can help to design wireless optical communication systems on modulation.