Low-total harmonic distortion (THD) and fast dynamic response of multiphase converters are the major challenges for high-order quadrature amplitude modulation (QAM) in low-frequency (LF) communication (30–300 kHz). This article proposes a single-step trajectory model predictive control (SST-MPC) for 100 kHz lager-signal multiphase converters, which improves the dynamic performance of optimized pulse patterns (OPPs). Low THD of multiphase converters at a steady state can be achieved by OPPs, which is well applied to LF communication. SST-MPC proposed in this article takes the transient trajectory into account and designs a new transient trajectory to reduce the settling time. Meanwhile, the first step and the second step predictive output voltage can be calculated in parallel only by the first step future multilevel output voltage. Even if the ratio of the control frequency to the output frequency is low, fast dynamic response and over/undershoot-free can be achieved by SST-MPC. The computational burden of SST-MPC is similar to the traditional single-step model predictive control (SS-MPC). Simulation and experimental results are given to verify the excellent dynamic performance of SST-MPC. Compared with the settling time of the two state-of-the-art SS-MPCs, the average improvements of SST-MPC are 37.02% and 30.24%, respectively.