A novel scheme of photonic aided vector millimeter-wave (mm-wave) signal generation without a digital-to-analog converter (DAC) is proposed. Based on our scheme, a 20 Gb/s 4-ary quadrature amplitude modulation (4-QAM) mm-wave signal is generated without using a DAC. The experiment results demonstrate that the bit error rate (BER) of 20 Gb/s 4-QAM mm-wave signal can reach below the hard-decision forward-error-correction threshold after a delivery over 1 m wireless distance. Because the DAC is not required, it can reduce the system cost. Besides, by using photonic technology, the system is easily integrated to create large-scale production and application in high-speed optical communication.