For example,app was not visible in the background,system need memory for other app and kill the app process,then user restart the app.Will the @Extra annotation restore the data automatically？
No. Extra is for extracting the extras from the Intents coming to your Activity. To save and restore fields you should use @InstanceState. You can annotate the same field which you already has @Extra.
BTW AndroidAnnotations is just a wrapper, so these concepts are coming from core Android.