The decision to cancel the event, which was due to take place in Corbridge, was made after further rain was forecast ahead of this weekend.
There were due to be hundreds of classic cars, motorcycles, vans, trucks and ex-military vehicles on display.
A show spokesman said: “It is with great regret that we have taken the decision to cancel the “Northumberland Classic Vehicle Show” due this Sunday, August 18, at Tynedale Park, Corbridge.
“Due to the continuous spell of wet weather (and now with more rain forecasted running up to the weekend), the ground conditions at the venue are poor and will not improve in time, to safely run the event.
“We have received an excellent large entry of pre-booked exhibits, but unfortunately the weather has beaten us this time. We will be back next year at Tynedale Park.”