This study reveals the physical mechanism behind anomalous surface incident solar radiation (Rs) attenuation in Beijing during the COVID-19 lockdown (February 2020). Sunshine Duration observations reveal the paradox of dimming event under strictest lockdown policies in February 2020 over Beijing. Modern-era retrospective analysis for research and applications, Version 2 (MERRA-2) reanalysis shows Rs decreased abruptly by 12.89 W·m−2 in February 2020 compared to 2015–2019 (pre-pandemic), which is confirmed by Himiwari-8 satellite retrieved Rs. Through multi-parameter attribution analysis, Shapley additive explanations indicated that an anomalous increase in aerosol optical depth contributed 31.700% to Rs attenuation, primarily driven by chemical formation of secondary organic aerosols that offset benefits from reduced primary emissions. Simultaneously, modified cloud physical properties collectively accounted for 38.02% to Rs attenuation. Specifically, doubled low cloud cover accounted for 23.89% while increased low cloud optical thickness contributed 13.52%. Further compounding these effects, weakened boundary layer dynamics exerted synergistic impacts: boundary layer height (BLH) compression (168.93 m) contributed 14.92% and reduced wind speed (0.63 m·s−1) contributed 9.51%, jointly promoting near-surface aerosol accumulation through suppressed pollutant diffusion. Additionally, elevated surface temperature (+1.36 °C) exacerbated Rs attenuation by facilitating aerosol nucleation and cloud condensation nucleus formation. Collectively, these findings challenge the assumption that emission reduction invariably improves Rs, ultimately confirming nonlinear climatic effects from coupled aerosol-cloud-Rs interactions under abrupt anthropogenic disturbances.