A generation scheme for terahertz (THz) quadrature phase shift keying (QPSK) signals over fiber based on on-off-keying (OOK) modulation is proposed. A pair of optical octave sideband signals is generated by a dual-parallel Mach-Zehnder modulator (DP-MZM), and two independent OOK baseband signals are modulated to two polarization states of the octave sideband signals by two intensity modulators (IMs). The two polarization signals are superimposed after phase and amplitude adjustment, and the superimposed optical signal undergoes photoelectric conversion at the terminal after power amplification and optical fiber transmission. THz QPSK signals are thereby generated. In the VPI simulation environment, the transmission performances of 80, 240, and 400 GHz signals are verified. The results show that the bit error rate (BER) of a QPSK signal with a baud rate of 20 GBuad and a frequency of 400 GHz generated by the proposed scheme is below the forward-error-correction threshold (3.8×10 ^-3) after the signal is transmitted over a 40 km zero dispersion shifted fiber (DSF). Our proposed scheme, with no need for pre-coding or a digital-to-analog converter, reduces the complexity of signal processing and system cost.