Charges were brought by Westminster City Council against the RHS after investigators found several serious problems at the London site.
It was found staff members were riding a "goods-only" hoist and wedging a metal bar in it to override the power button. A 19-year-old man lost four toes and half his big toe while travelling on the hoist in March last year.
In detail, the RHS was fined: £7,000 for failing to provide and maintain a safe system of work concerning the operation of the "goods-only" hoist; £7,000 for failing to provide information, instruction and supervision about the hoist; £1,000 for failing to have a suitable and sufficient risk assessment; and additionally ordered to pay £15,000 costs to the council.
An RHS representative said a review of health and safety procedures and the hoist's operating system was carried out, and a report was commissioned from an external lift maintenance firm on possible alterations. Those design and operation recommendations were implemented and the RHS has changed the way the hoist is used.
The representative pointed out the case was the only serious accident known to have occurred in the past 100 years of operating events in the halls and other RHS show venues.
Westminster councillor Audrey Lewis said: "This tragic accident was entirely avoidable and as a consequence the life of a young person with a promising future football career has been permanently affected.
"This case sends an important message to employers that proper management of health and safety is paramount."