The organisers of the Royal Welsh Show say it made a surplus of nearly £390,000, despite bad weather.
The Royal Welsh Agricultural Society said the successes of its two other annual events at the Powys showground helped make a total surplus of more than £630,000.
The society is spending thousands of pounds developing the showground, and a new £1.7m food hall will open in July.
The main ring will also be resurfaced after it turned to mud in 2009.
The society said the flagship Royal Welsh at Llanelwedd, as well as the Smallholder and Garden Festival and the Winter Fair all made money.
The society promises an "extensive programme" of spending on the showground and facilities to enhance its reputation "as one of the world's leading agricultural societies".
Chairman of the board of management, David Lewis said: "We are a major player in the premier league of agricultural shows attracting hundreds of thousands of visitors every year to Llanelwedd.
"If we are to maintain this position investment in the showground, our chief asset, is essential.
"That is why substantial surpluses like those for 2009 are key to our future success."
A large amount of the society's income was held in restricted funds, meaning it was not for general use but ring-fenced for projects for which it was raised in the first place, said Mr Lewis.
The most costly of these is the new food hall, costing £1.77m.
After this year's show it is hoped a new Montgomery members pavilion will be built.
The third major scheme is the resurfacing of the main ring. An artificial surface will also be laid in the nearby collection ring.