To better utilize the optical fiber bandwidth and enhance the communication capability of the RoF system, this paper combines photonic vector modulation and optical millimeter-wave generation techniques, proposing an 18-fold frequency 16 quadrature amplitude modulation (QAM) millimeter-wave generation scheme based on polarization division multiplexing (PDM). The system consists of two parallel modules: frequency doubling and vector modulation. In the frequency doubling module, two dual-parallel Mach-Zehnder modulators (DP-MZM) and an optical phase shifter are used to generate the ±6th-order optical sidebands. After passing through a semiconductor optical amplifier (SOA), four-wave mixing effects are induced, and the 18th-order sidebands are obtained through filtering. In the vector modulation module, eight 10 Gbit/s binary NRZ signals drive the DP-MZM, and polarization multiplexing technology is applied to implement 16QAM optical domain modulation on two orthogonal polarization directions. The PDM-16QAM signal is coupled with the 18th-order optical sidebands and, after photodetection, an 18-fold frequency PDM-16QAM signal is generated. Simulation analysis shows that when the photodetector's received power is ?25 dBm, the signal-to-noise ratio (SNR) of the system is greater than 20.5 dB, and after 30 km transmission through single-mode optical fiber, the system performance remains good. Even when there are fluctuations in the SOA injection current and laser linewidth within a certain range, the bit error rate (BER) of the system remains below 3.8×10^?3.