A novel system for frequency-doubling microwave signal generation with tunable phase shift based on a dual-polarization quadrature phase shift keying (DP-QPSK) modulator which includes two dual-parallel Mach-Zehnder modulators (DPMZM) is proposed and demonstrated. The radio frequency (RF) signals drive the top DPMZM for generating a negative first-order RF sideband on the X-polarization state and drive the bottom DPMZM to obtain a positive first-order RF sideband on the Y-polarization state. After that, the two first-order sidebands enter a three wave-plates polarization controller (PC) of half-quarter-quarter (HQQ) wave plate type and then their phases are controlled. After a polarizer and a photodiode (PD), a frequency-doubling microwave or millimeter-wave signal with tunable phase shift is produced. The results indicate a full 360-degree phase shift is realized, in the meantime, the phase deviation is less than 1-degree and amplitude deviation is no more than 0.3dB.