The site on car park six will allow heavy goods vehicles to be checked and cleared before heading south to ports including Dover and Folkestone.
West Midlands Police has warned of an increase in traffic around the airport when the site opens on January 1.
It has also emerged that police officers from the region will be dispatched to Kent to help deal with a potential increase in traffic at ports should Britain and the EU fail to reach an agreement by December 31.
The run-up to Christmas has already seen chaotic scenes at ports, with long queues forming due to extra traffic brought on partly by Brexit stockpiling and demand for Covid medival supplies.
With a Brexit deal yet to be agreed, Ministers have moved to bring in inland border facilities in a bid to speed up the flow of traffic.
Detective Chief Superintendent Chris Todd revealed plans for the region at a meeting of the West Midlands Police and Crime Commissioner's strategic board.
He said: "There will be an inland border facility in the Birmingham area. That will be dealing with traffic outbound destined for Kent.
"There will be an opportunity for HGVs to stop at a facility in Birmingham to clear customs, effectively, to speed up the transition once they reach the ports.
"We're preparing for that with partners, and for the potential increase in traffic that we can see from that.
"And we have received some mutual aid requests, so we know that we will need to send some officers down to Kent in order to assist with traffic at the border on January 1."
In an internal blog Det Ch Supt Todd said the customs site would be at car park six of Birmingham Airport.
He added that a no deal Brexit would impact the way the force deals with international criminals unless police were allowed continued access to information currently shared with the EU.
Labour PCC David Jamieson said: "A no deal Brexit will have a major impact on policing. Police forces rely on the exchange of data to help apprehend some of society’s most vile individuals.
"It would be perverse that if as a result of ‘taking back control’ violent criminals and rapists find it easier to cross borders with impunity.
"I am also dismayed that whilst we are dealing with rising crime and Covid, some West Midlands Police officers will have to travel to Kent to help local authorities deal with the potential chaos at the port.
"West Midlands Police is not short of work, and Brexit is only adding to it."