jqGrid - How to modify form_editing construction?

Solution 1:

There are rowpos and colpos properties of formoptions which would be helpful for you.

The demo demonstrate how you can change the standard editing form created by jqGrid to the following

If I understand correct your problem the usage of rowpos and colpos could be very helpful in your case.

Solution 2:

If you need to customize the form, your best bet may be to create your own page and use a plugin such as jQuery UI Dialog to display your custom form. It will be more work since you cannot use the built-in form editing capabilities of jqGrid, but you will have complete control of the layout of the form.