The high-speed single-channel transmission of nonreturn-to-zero differential phase-shift keying (NRZ-DPSK) signal is demonstrated using fiber loop. The 414 km fiber loop is divided into four spans,which consist of standard single-mode fiber (SSMF) and dispersion compensation fiber (DCF),and erbium-doped fiber amplifier/distributed Raman amplifier (EDFA/PRA) are used for hybrid amplification. The optical spectrum and eye diagrams of 42.8 Gb/s DPSK signal are obtained after 414 km,828 km and 1242 km transmission. The curves of bit error rate (BER) of the DPSK signal are given both in back-to-back configuration and after transmission using single-ended detection. The BER is 6.3×10-4 after 1242 km transmission,and the error-free transmission can be realized using enhanced forward error correction (FEC).