The possible application of multi-phase modulation technology in optical fiber communication based on Carrier-Suppressed Return-to-Zero (CSRZ) format was studied.With analyzing the characteristics of CSRZ format, Differential Quadrature Phase Shift Keying (DQPSK) and Eight Differential Phase Shift Keying (8DPSK), formula of CSRZ-DQPSK and CSRZ-8DPSK modem methods was got and the methods in their specific achieving processes were presented.Spectra based on CSRZ, CSRZ-DQPSK and CSRZ-8DPSK modulation methods and their eye diagrams following demodulator using Matlab simulation were obtained.The results show that the CSRZ-DQPSK and CSRZ-8DPSK modulation methods, as the possible new methods, had narrower spectra with higher spectrum efficiency.Their performance of eye diagrams was also much satisfactory after demodulation, suggesting some possible applications of the methods in the next generation of optical fiber communication.