A novel scheme to generate microwave phase-shifting signal with an adjustable frequency-multiplication factor based on polarization division multiplexing dual-parallel Mach-Zehnder modulator is proposed. Without filters, the scheme can generate frequency-doubled, frequency-quadrupled, frequency-sextupled, or frequency-octupled microwave signals by changing the radio frequency drive signals and direct current bias voltages of the modulator. By simultaneously controlling the angle between the polarizer and the principal axis of the modulator, the phase can be continuously adjusted from 0° to 360°. The simulation results show that a 5-GHz radio frequency signal can be converted into full-range linear phase-shifting microwave signals with the frequencies of 10 GHz, 20 GHz, 30 GHz, and 40 GHz. Their power fluctuation is less than 0.5 dB when the phase changes continuously. Moreover, it also shows that the scheme has good frequency tunability. In addition, the operating frequency range of the scheme as well as the influence of modulator extinction ratio, direct current bias voltage drifting, electrical phase shifter amplitude, and phase imbalance on the system performance are studied and analyzed.