In this paper, we propose a W-band 8-quadrature-amplitude-modulation (8QAM) frequency tripling photonic vector millimeter-wave (mm-wave) signal generation method by using a phase modulator (PM) with only amplitude pre-coding. The PM is driven by 2-Gbaud 8QAM-modulated amplitude precoded signal at 25 GHz. Instead of phase pre-coding, we only need to reverse the real part of the signal at the receiver after photo detector (PD). The structure of the transmitter and the structure of the receiver are simple. The frequency tripling scheme is completed by numerical simulation, the output optical spectrum is consistent with the theoretical analysis, and bit-error-ratio (BER) curves indicate that the put forward 75 GHz 8QAM vector signal generation technique has good performance. The BER of 6 Gbit/s 75 GHz 8QAM vector mm-wave signal is below 3.8 × 10 −3 after 12 km optical fiber transmission. For all we know, it is the first time to report on the generation of high-order QAM photonic mm-wave signal with odd times of RF frequency by using a single external modulator. INDEX TERMS Millimeter wave, frequency multiplication, phase modulation, digital signal processing, quadrature amplitude modulation. LUN ZHAO received the M.S. degree in communication and information system from the Wuhan Research Institute (WRI), Hubei, China, in 2012, and the Ph.D. degree in electronic science and technology from the School of electronic engineering, Beijing University of Posts and Telecommunications, Beijing, China, in 2016. He is currently working in information and telecommunication engineering with the Ubiquitous Wireless Communication Technology Team, Chongqing University of Posts and Telecommunications. His research interests include radio over fiber, coherent optical communication, machine learning/deep learning in optical communication, optical physical layer security, and 5G mobile networks. LIAN XIONG was born in Huanggang, Hubei, China, in 1985. He received the B.S. degree in telecommunications engineering from the North University of China, Taiyuan, China, in 2008, the M.S. degree in communication and information system from the Taiyuan University of Technology, Taiyuan, in 2011, and the Ph.D. degree in communication and information system from