A simple reconfigurable direct digital modulation system with time-modulated metasurface is proposed and verified. Instead of baseband transmitting chain, baseband complex symbols of multiple users are mapped into the harmonics of control signals and load to the radio frequency (RF) carrier by the metasurface with only 1-bit phase-adjusted resolution. Theoretical analysis and simulations are provided to verify its feasibility. The reconfigurable harmonic modulation method, low complexity hardware and minimum requirement for metasurface indicate its potential applications in large scale multiple-input multiple-output (MIMO) transmitters.