@vishvajeet-smboo 

"while the cash basis method considers bill payments and updates inventory positively, the same trend is not reflected for invoices. Consequently, the inventory keeps increasing under the cash basis method."

If your inventory is increasing on cash basis, then you must not be using items on your bills or your inventory asset account is being increased some other way that bypasses inventory items (expense/check entry, journal entry, etc. that posts directly to your inventory asset account).  QBO disregards items on cash basis reports.