How can i get a orbit in ECI coordinate, as the CESIUM is in WGS-84 coordinate

I got a sat orbit from SGP4 program, which is under True Equator Mean Equinox coordinate system, while the CESIUM is using WGS-84 coordinate system, can i change the coordinate system that CESIUM using?

There’s no way to change the coordinate system that CesiumJS is using - I would recommend converting your coordinates before loading them in your app. This is what Cesium ion does with most data uploaded, to pre-process them in that way.