The agency has reaffirmed its negative ratings outlook for WA after warning in December that the state's debt burden was putting its AAA credit rating at risk.
He says the government needs to show financial restraint, particularly with its big ticket election items.
"The fact is that there's no magic pot of money here, money isn't limitless, and we should be making decisions about investment and infrastructure based on what is best for the state," he said.
Mr Pearson says the Government needs to show financial restraint.
"If we lose the AAA rating, it'll cost taxpayers more money because it'll cost the government more money to borrow money," he said.
"We have to strike a balance between investing to support a growing state economy, a growing state population, and protecting our AAA credit rating," he said.
"That's what we've been doing, and that's what we'll continue to do."
In 2008, WA had a debt level of $3.6 billion, according to Treasury figures.
It then rose to just over $12 billion in the 2010/2011 financial year.
The debt will be $18 billion at the end of the 2012/13 financial year.
It is then projected to be $23 billion in the 2014/2015 forward estimates.
Mr Buswell says the economy is in good shape.