The orbital angular momentum is an electron’s essential degree of freedom and provides an alternative opportunity for the further development of spintronics. Recent studies suggest orbital transport as a potential tool to realize practical and highly-efficient spin manipulation with diverse material classes. Nevertheless, utilization of the orbital transport remains a challenging issue considering that the orbital transport often bares distinctive properties to the spin transport. Here we study the role of oxygen atom accumulation on the orbital transport in CoFe/Cu/Al2O3 ultrathin structures. By varying the type of oxygen accumulation, we revealed that the gradient of the oxygen accumulation nearby the CoFe/Cu interface can be a crucial factor of the orbital transport, modulating the orbital torque by a factor of about ~3. Our finding will encourage to realize efficient and versatile utilization of orbital transport for nano-spintronic devices.