primitives.add(new Cesium.Primitive(\{  
geometryInstances: ,  
releaseGeometryInstances:false,  
appearance: new Cesium.PerInstanceColorAppearance()  
\}),100);

重点:releaseGeometryInstances:false,

由于Cesium使用primitive加载数据性能考虑,会自动清空原来的geometryInstances,设置即可。