Abstract: Using ground-based ozone (O₃) measurements, the ERA5 reanalysis data from the European Center for Medium-Range Weather Forecasts, and the WRF-Chem numerical model, this study investigated the impact and mechanisms of wildfires in eastern Siberia on surface O₃ anomalies in Northeast China in July 2014. The results indicate that (1) Wildfire smoke from eastern Siberia can reach and accumulate in Northeast China. This is caused by the interaction among three key weather systems: an extratropical cyclone moving eastward in the westerlies at mid–high latitudes, a high-pressure ridge to its west, and the northward-moving Typhoon Matmo. The northerly wind on the western flank of the extratropical cyclone transports wildfire smoke southward through the free atmosphere. The downward flow ahead of the high-pressure ridge brings the smoke into the near-surface layer over Northeast China. The airflow along the northern edge of the northward-moving Typhoon Matmo inhibits the eastward transport of smoke, leading to its retention and accumulation in Northeast China. (2) Various locations in Northeast China were affected by the transport of upstream wildfire smoke and successively experienced surface O₃ pollution events from July 25 to 29. The positive anomaly of O₃ concentration reached its maximum during the daytime on July 27. The comparison experiments of WRF-Chem with and without wildfires confirmed that, with other conditions unchanged, wildfire smoke can increase the local O₃ concentration in Northeast China by up to 40%. (3) The atmospheric composition and reaction rates in the comparison experiments showed that the abnormal increase in O₃ concentration during the daytime on July 25 and 26 is primarily attributed to the increase in the concentration of peroxy radicals (HO₂) induced by the high concentration of carbon monoxide (CO) transported by wildfires. The O₃ peak during the daytime on July 27 is associated with three factors: the maximum increase in CO concentration, the abnormal increase in formaldehyde secondarily generated in the wildfire smoke, and the elevated HO₂ concentrations produced from HCHO oxidation.