About the coordinate system

I would like to know what coordinate system Cesium For Unity uses, and if it is connected with point data generated in other GIS systems, is there any conversion method available

I’m not sure if I totally understand what you’re trying to ask. But I think the important points are:

  1. Cesium for Unity is primarily used to render 3D Tiles.
  2. 3D Tiles are almost always WGS84 Earth-Centered, Earth-Fixed Coordinates (3d-tiles/specification at main · CesiumGS/3d-tiles · GitHub), and Cesium for Unity generally assumes this to be the case.
  3. ECEF 3D Tiles are transformed into Unity world coordinates by the CesiumGeoreference component.
  4. Cesium for Unity also supports raster overlays, which are 2D pictures draped over 3D Tiles. Those can be expressed in either EPSG:4326 or EPSG:3857.

For example, I have a set of latitude and longitude data of vehicle trajectories, in the project based on Arcgis For Unity, the trajectory is in the lane, but the same trajectory, in the project based on Cesium For Unity, has offset

Is there a Position offset on the Transform component of your CesiumGeoreference or Cesium3DTileset, perhaps? Usually Position and Rotation should be all zeros, and Scale should be all ones.