Transboundary air pollutants deteriorating ambient air quality has become an emerging international concern problem recently. This study analyzed and simulated an air pollution case of forming high-concentrated particulate matters (PMs) caused by a severer dust storm case during January 17 to 19, 2014. For this case, concentrations of PM10 and PM2.5 reached up to 680 and 165 µg m–3, respectively. Those concentrations were 5–10 folds higher than the proposed ambient air quality standards of Taiwan. The mechanisms for forming high-concentrated PMs in the ambient air of Taiwan and its surrounding area were investigated. Based on the monitored pollutant concentrations and the simulation results with the Weather Research and Forecasting- Chemistry (WRF-Chem) model, both structures of meteorological conditions and mechanisms for forming high-concentrated PMs were analyzed. The long-range transported-in air pollutants, travelling with the movement of a strong continental cold high-pressure system originating from northern China, contributed to the poor ambient air quality. Two important mechanisms for forming this high concentration PM case were proposed, including the transported-in transboundary air pollutants (or their precursors) from China and leeward side effects on the west side of The Taiwan Island. Low inversion layers in the atmosphere and terrain downwash near the ground surface was observed in this case study while continental cold air approaching. The WRF-Chem model simulation results confirmed that the ambient air of western Taiwan was dry and moved downward during the investigated period. Hence, the contribution of transboundary air pollutants to deteriorate ambient air quality cannot be ignored.