you should use form inside your modal panel and should not include the modal to the external form.
thank you for you replay .but it still doesn't work.
it seems as the modalpanel covers the suggestbox's div.
Why do you set zindex attribute of modalPanel?
Thank you for your suggestion.I have solved the problem.
because i set the zindex too large.
just change the modalpanel's zindex to a lower number,and set the suggestionbox's zindex larger than modalpanel's.