>
>I use ANT profiler to trace the memory, and I found that some objects is not released (new object created) after every postback.
>
>1. MyBO.SomeEvent
>2. Button
>3. MyDataGridView
>
>Question: How could I free up them upon every postback? In which event/method should I place code to nullify the child object?
>

Try unhooking the event handler from your business object in the Page_Unload(). It's probably keeping the business object from being cleaned up by the GC. You can also set your property to null here if you want (although it shouldn't be necessary).

protected void Page_unLoaded(object sender, EventArgs e)
{ 
   this._myBO.SomeEvent -= this.MyBO_SomeEvent;

}