Basing on the 1-second sounding data from L-band radar and the daily max potential surface air temperature over Beijing, the possibility of deriving the daily maximum mixing layer height (MMH) over Beijing region by the parcel method was studied. By comparing the inversion results of the 1-second sounding data and the conventional sounding data at local time 08:00 with the inversion results from a micro pulse lidar (MPL), it is found that the consistency between the former and the MPL results is better than the latter. The reason for the larger bias from the conventional data results may be due to their lower vertical resolution. By comparing the inversion results of the 1-second sounding data in spring, summer, autumn and winter respectively with the results from the MPL, it is found that the consistency is better in spring, summer and autumn, but it is worse in winter. Long-term data results of the MMH over Beijing area from 2010 to 2017 were obtained using the 1-second sounding data at local time 08:00 and the daily maximum potential surface air temperature. It is found that the MMH almost showed a decreasing characteristic from spring to summer, to autumn and to winter successively. With the long-term results, it is found that the thermal stability defined by the difference of the daily max surface air temperature and temperature at the layer of 850 hPa was strongly positively correlated with the MMH in Beijing area.