Abstract: Sulfate (SO₄²⁻) and black carbon (BC) can modify the energy budget of the earth–atmosphere system by scattering or absorbing solar radiation, thereby causing changes in local thermal and cloud processes and affecting the atmospheric circulation and climate system. As one of the subsystems of the East Asian summer monsoon, the South China Sea summer monsoon (SCSSM) considerably affects the East Asian atmospheric circulation and precipitation. However, the influence of SO₄²⁻ and BC on SCSSM and its mechanism are not yet fully understood. Therefore, this study employs the community earth system model CAM5.1 module to study the effects of SO₄²⁻ and BC on the meridional sea–land thermal difference between the South China Sea and South China, convection in the Indo–China Peninsula, breakup of the western Pacific subtropical high, and onset of the SCSSM. The dynamic and thermodynamic mechanisms of aerosols that affect the onset of SCSSM are emphasized. The simulation results show that SO₄²⁻ and BC can effectively enhance the stability of the entire troposphere in the Indo–China Peninsula, triggering anomalous subsidence airflow over the Peninsula, dynamically inhibiting convection in the Peninsula, and causing a delay in subtropical high belt breakup by 2 (SO₄²⁻) and 1 (BC) pentads, from late spring to early summer. In addition, the reversal time of the spring meridional sea–land temperature difference was delayed/advanced by SO₄²⁻/BC. Consistent dynamic and thermal effects of SO₄²⁻ delay the onset of SCSSM by 1 pentad. Meanwhile, BC exerts insignificant effects on the onset of SCSSM, probably because of the opposite dynamic and thermal effects of BC.