Abstract: The observation data of five national basic（quasi） stations in Hebei from 2017 to 2019 were used. Both national standard method and NOZAKI method were used to calculate and analyze the height of mixed layers. The results showed that the mixing layer height was the lowest in the mountainous area. It was higher in the coastal area,and the highest was found in the southern plain area. Compared with the national standard method, the height and frequency distribution of the mixed layer calculated by NOZAKI method was more uniform and the distribution area was larger. The height of mixing layer calculated by the national standard method was mainly related to the wind speed of 10 meters. The height of mixing layer calculated by NOZAKI method was not only related to wind speed, but also has a negative correlation with humidity of over 80%. The daily variation of each region was of single peak type, and the calculated height by NOZAKI method was closer to the reality in terms of time variation rule. The distribution frequency of the height by NOZAKI method seemed more even with wider area. There was a higher correlation between the height and the PM_2.5 concentration. The formula of PM_2.5 concentration calculation fitted from the mixing layer height and PM_2.5 concentration was more suitable in the plain area, rather than the costal and mountainous area.