Translink said the buses will operate from 8.30am to 9pm at Lisburn train station between 15 and 17 May, leaving every 10 minutes at peak and every 20-30 minutes off peak.
There are also Goldline coaches offering a combined package of travel and admission ticket.
Meanwhile, three morning trains coming from the North-West will run through to Lisburn so that passengers will not need to change trains in Belfast.
"These include the 7.13am departure from Derry~Londonderry and the 7.05am and 9.05am departures from Portrush," Translink said.
"Due to anticipated heavy congestion around the site, passengers are advised to allow at least an hour transfer time for returning from the show to make onward bus and train connections."
The show - one of the biggest events in the farming calendar - opens on Wednesday on the Maze site after 100 years of being staged at the King's Hall in south Belfast.
Colin McDonald from the Royal Ulster Agricultural Society encouraged anyone visiting the show to consider using public transport to help reduce traffic congestion.
"The infrastructure that's in place will do for the Balmoral Show but of course the overall site will need more infrastructure than what is there at the moment," he said.
"But we can manage on Wednesday. There is a traffic management plan in place and everybody can look at the media and look at the website and plan how best to get to the show now, of course public transport, we think, is the best way."