【解决办法】使用ScreenSpaceEventHandler中setInputAction的MOUSE_MOVE方法。参考代码如下：
var screenSpaceEventHandler = new Cesium.ScreenSpaceEventHandler(scene.canvas);
screenSpaceEventHandler.setInputAction(function(movement) {
//最后的屏幕坐标
var haveEn = viewer.scene.pick(movement.endPosition);
if(viewer.scene.pickPositionSupported && Cesium.defined(haveEn) && haveEn.id !== ' '){
clearAlpha();
if(haveEn.id.polygon !== undefined){
var haveEnsNow = haveEn.id.polygon._material._color.getValue();
haveEnsNow.alpha = 1;
haveEn.id.polygon._material._color.setValue(haveEnsNow);
}
}else if(haveEn == undefined){
clearAlpha();
}
}, Cesium.ScreenSpaceEventType.MOUSE_MOVE);
function clearAlpha(){
for(var i=0;i<viewer.entities.values.length;i++){
if(viewer.entities.values[i].name == "yanse"){
var haveEnsLast=viewer.entities.values[i]._polygon._material._color.getValue();
haveEnsLast.alpha = 0.2;
viewer.entities.values[i]._polygon._material._color.setValue(haveEnsLast)
}
}
}
