We propose a theoretical mechanism and new coding strategy to realize extremely accurate manipulations of nonlinear electromagnetic harmonics in ultrawide frequency band based on a time-domain digital coding metasurface (TDCM).Using the proposed mechanism and coding strategy,we design and fabricate a millimeter-wave (mmWave) TDCM,which is composed ofreprogrammable meta-atoms embedded with positive-intrinsic-negative diodes.By controlling the duty ratios and time delays of the digital coding sequences loaded on a TDCM,experimental results show that both amplitudes and phases of different harmonics can be engineered at will simultaneously and precisely in broad frequency band from 22 to 33 GHz,even when the coding states are imperfect,which is in good agreement with theoretical calculations.Based on the fabricated high-performance TDCM,we further propose and experimentally realize a large-capacity mmWave wireless communication system,where 256 quadrature amplitude modulation,along with other schemes,is demonstrated.The new wireless communication system has a much simpler architecture than the currently used mmWave wireless systems,and hence can significantly reduce the hardware cost.We believe that the proposed method and system architecture can find vast application in future mmWave and terahertz-wave wireless communication and radar systems.