An $18 million tax break for Crown Perth is designed to help attract high-roller gamblers and pay the West Australian Government more tax, Treasurer Mike Nahan says.

The break, which was unveiled in Thursday's budget, sees an additional $18 million allocated over three years for a rebate to draw in big-spending gamblers.

It comes as the Government blames declining revenue for the debt and deficit problems unveiled in Thursday's budget.

The budget papers show a drop in Government revenue - from a projected $31.2 billion in 2014-15 to an expected $25.6 billion in 2016-17 - and an almost halving of projected casino tax revenue.

The Government expects to collect $67 million in casino tax this financial year, although two budgets ago the Treasury estimated it would receive $127 million.

The budget papers said the rebate would help to generate extra revenue for the state by stimulating high-roller betting activity.

Dr Nahan described it as a "reorientation of the tax imposed on high rollers".

He said the rebate was also important in making Crown Perth more competitive in the domestic and international markets.

"The objective is for Burswood to go out and attract more of them to pay more tax," Dr Nahan said.

"And they were meeting competition from Singapore and Macau, and we did nothing more than match what they did at the casino in Melbourne and Sydney."

The rebate is the latest high-roller tax break handed to Crown Perth, even though it has been posting strong results in its VIP gaming operations.

In 2014-15, when the Government agreed to cut its international commission business tax rate from 11 per cent to 8 per cent, the casino's VIP revenue grew by 44 per cent to $250 million.

Between July and December last year, Crown Perth's high-roller revenue grew by 28 per cent to total $118 million.

Racing and Gaming Minister Colin Holt was unavailable for comment.

In a written statement, a spokesman for Mr Holt said the growth in high-roller revenue showed that the lower high-roller tax rates were attracting gamblers to WA.