Tengchong is located in the Yunnan-Guizhou Plateau with complex terrain and is a typical mountain city. The planetary boundary layer (PBL) and its cross-border transport of pollutants caused by its special geographical location urgently need attention, so it is of great significance to study the long-term boundary layer structure and the changing characteristics of meteorological conditions in Tengchong. In this paper, the L-band radiosonde data of Tengchong and the atmospheric boundary layer height (PBLH) calculated by Richardson number method are used to verify the ERA5 reanalysis data. Based on the ERA5 reanalysis data, the temporal characteristics and influencing factors of PBLH in Tengchong during 1980-2023 are analyzed by statistical method. The results indicate that the PBLH of ERA5 has a good correlation with the observed PBLH in Tengchong, and the average PBLH of ERA5 is 3.7m and 279.4m lower than the observed PBLH at 08:00 and 20:00, respectively.The PBLH in Tengchong showed significant fluctuations, with an upward trend in summer and autumn (0.7 m/yr, 0.2 m/yr), a downward trend in spring and winter (-0.1 m/yr, -0.2 m/yr), and an upward trend in dry and wet seasons (0.05 m/yr, 0.3 m/yr). PBLH was the order in spring (1504m) > winter (871m) > Autumn (572m) > summer (468m) at daytime, while at night, PBLH was the order in summer (52m) > Autumn (23m) > Spring (27m) > Winter (19m). PBLH in wet season (44m) was higher than that in dry season (21m). PBLH fluctuates greatly during the daytime and is relatively stable at night, reaching the daily peak at 14:00 or 15:00 in the afternoon. The PBLH can exceed 3500m in dry season and 2000m in wet season. The daily PBLH fluctuates the most in spring and dry season. On the annual scale, PBLH was positively correlated with 10m wind speed, surface sensible heat flux, ground-air temperature difference, surface temperature and 2m air temperature, and negatively correlated with relative humidity, total cloud cover, surface latent heat flux and 2m dew point temperature. On the seasonal scale, the PBLH in spring, autumn, winter and dry season was mainly driven by 10m wind speed, while in summer and wet season it was mainly driven by high latent heat flux, total cloud cover, relative humidity and low sensible heat flux. In the diurnal variation, 10m wind speed, surface sensible heat flux and relative humidity in daytime were the main factors affecting the development of PBLH, while the surface latent heat flux at night was the only significant factor affecting the development of PBLH.