Lithosphere effective elastic thickness (Te) is a term on the bases regional isostasy and flexure theories of lithosphere. This paper firstly outlined the development of the isostasy, and then described the concept and characteristics of Te. It was emphasized that Te was a subject closely related to geology and geophysics since the Te was not only calculated by the spectrum analysis on the bathymetry and gravity data, also related to the geological, thermal, rheological structures. Te could provide us with the physical properties of lithosphere. However, Te merely was an equal and effective strength of lithosphere, and it could not be compared with the seismic and geo-electronic-magnetic thickness values of crust or lithosphere. But the yielding strength envelop (YSE) of lithosphere could compare the two kinds of thickness. The theoretical calculations of ocean and continental YSEs showed that the Te was obvious less that seismic thickness. Particularly, for the continent, the crust thickness, thermal age and strain rate significantly had strong effect on the lithosphere strength. Finally, taking western Yunnan as an example,the paper briefly introduced a new way to calculate the curve of coherence value to wave number, and discussed the latest progress of lithosphere Te.