Thank you Farshad for your works! Anyway I test and I still found some problems. Here is the Position property of the form I set.
poDesigned - It's OK
poDefault - It's OK
poDefaultPosOnly - It's OK
poDefaultSizeOnly - It's OK
poDesigned - It's OK
poMainFormCenter - It's OK but the form is displayed Left Justified the same as all above OK condition but it's not in the center.
poOwnerFormCenter - It's OK but the form is displayed Left Justified the same as all above OK condition but it's not in the center.
poDesktopCenter and poScreenCenter - Still not OK because the form is displayed in the center of the browser area but you can not display the top of the form even you move the vertical scrollbar to fully top position.