Abstract: Using the daily mass concentrations of PM_2.5, PM₁₀, NO₂, SO₂, CO, and O₃ and the corresponding meteorological data from December of 2018 to February of 2019, the characteristics and influencing factors of air pollution in Northwest Shandong province were analyzed. The results show that in the winter of 2018, air pollution is relatively serious in Northwest Shandong province. In Liaocheng, Dezhou, and Binzhou, the number of days with mild or above pollution is 61%, 60%, and 54%, respectively, and the number of days with severe or above pollution is 24%, 11%, and 9%, respectively. The main pollutants include PM_2.5, PM₁₀, and NO₂, among which PM_2.5 accounts for more than 60%. The diurnal variation of PM_2.5, PM₁₀, SO₂, NO₂, and CO shows a double-peak and double-trough pattern. The diurnal variation of PM_2.5, PM₁₀, SO₂, NO₂, and CO shows a double-peak and double-trough pattern. The diurnal variation of PM_2.5, PM₁₀, SO₂, NO₂, and CO appears at 04:00-07:00 and 15:00-17:00, respectively, and the peak value is lower in the afternoon than in the morning. O₃ presents a unimodal distribution, with a minimum value at 09:00 and a maximum value at 18:00-19:00. PM_2.5 is the main primary pollutant in the northwest of Shandong province. It is significantly positively correlated with PM₁₀, CO, and NO₂, and reaches the significance test of 0.01 level. The correlation between PM_2.5 and NO₂ at low relative humidity (< 60%) is higher than that at high relative humidity (≥ 60%), and its correlation with CO at high relative humidity is higher than that at low relative humidity. The average relative humidity and temperature in the polluted period (PM_2.5>75 μg·m^-3) are significantly higher than those in the clean period (PM_2.5 ≤ 75 μg·m^-3), and the wind speed and air pressure in the clean period are significantly higher than those in the polluted period.