In order to make the terrain look close，Cesium added a strip under the terrain.But now how do I cancel it
I don’t think its configurable by the API, but you can edit the source code to remove it.
If you are using the CesiumTerrainProvider, find the line that says:
var skirtHeight = provider.getLevelMaximumGeometricError(level) * 5.0;
and change 5.0 to 0.0.
Other terrain providers may have something similar.
Additionally, this new pull request includes support for changing the skirt heights, see the section on skirtRatio options.
Thanks very much！You're right