A novel microwave waveform generator based on a dual-polarization quadrature phase-shift-keying (DP-QPSK) modulator is proposed and experimentally demonstrated in this paper. The X-QPSK modulator is modulated by a local oscillator signal. For XI Mach-Zehnder modulator (MZM), odd sidebands are eliminated; for XQ-MZM, even sidebands are eliminated, while the Y-QPSK modulator is not modulated. Triangular or square waveforms can be generated by biasing the X-QPSK and adjusting the polarization controller properly. 3 GHz and 6 GHz triangular and square waveforms are successfully generated by experiment. The scheme does not need a high modulation index (m=1.25 in this paper). In addition, it features low cost and a simple structure without a filter or phase shifter.