>Hi..
>how about if the control isnot in master?

What kind of scenario is this? ContentPlaceHolder is really just meant for master pages. However, if you are using it some other way you can use the FindControl method of it to get a reference to the control inside of it. Just realize that FindControl will only find the textbox if it's a child of the ContentPlaceHolder and not nested deeper inside of some other control.

// Replace ContentPlaceHolder1 with the actual name of it
TextBox text = this.ContentPlaceHolder1.FindControl("txtMyTextBox") as TextBox;

if (text != null)
{
   //
}