I believe this information defaults from the Item setup...Is the item that you are selecting on the Requisition marked as an Inventory Item in Item Setup for the Org that you are creating the Requisition?
Your best solution may be a personalization or pcg rule on the requisition to ensure that the destination type is Inventory if there is an item selected. It can be made to set the destination type automatically, put up a message box telling the user the issue, or do both of those things.
You can test in your test instance, but most fields on the PO are required to match the requisition, so it may not be possible to change it on the PO. Even if it is possible to change it on the PO, its still better to catch it at the requisition level so you don't have to worry about catching PO's before they are approved or received. As background, users are allowed to select expense destination even with items on the line because some companies expense parts used by Engineering or for destructive quality testing.
The destination type can be expense or inventory for inventory items. If the item is delivered to an end user then the destination is considered expense destination, but if the item is delivered to an inventory stock location then the destination type is inventory. The deliver to location defaulted or chosen during check determines whether the item is delivered to inventory or expense destination. Choose a different deliver to location to see the differences.
If the item is inventory in Item Definition then the destination type will always be used as inventory
If the item is expense in item definition then the destination type can used either expense or inventory
Thanks for you detail explanation in this regards,
I have a last query regarding the issue which we have been facing, when user select any specific item on requisition form with destination is shown as "inventory" automaticall, however, after approval of requisition and Po, system automatically mark Destination Type as expense in few case,
is it pertaining to any bug or any thing else.