The subject of the present study is to analyze the characteristic variations of the ionospheric slab thickness observed at Lunping Observatory. The slab thickness data obtained from March 1977 to February 1982 were used to analyze the diurnal, seasonal, and solar cycle variations. The diurnal variation showed an unusually large peak that appeared in pre-sunrise hours, especially during winter time Lunar variations of slab thickness were obtained by Chapman-Miller method and discussed. The storm time variation and disturbance daily variation of slab thickness were obtained by selecting 138 strong and weak geomagnetic storms. Superposed epoch method was also used to analyze the geomagnetic activity effect on the variation of slab thickness.