The prince was criticised after revelations he had written to several ministers about issues such as the countryside and bureaucracy.
But the prime minister has told the BBC he finds the correspondence "helpful and informative" and should be encouraged.
Mr Blair also denied the letters had been leaked to a Sunday newspaper by anyone in his government.
The Prince of Wales has reportedly written to Mr Blair to express "regret" about the disclosures.
A newspaper claims the prince absolved Downing Street of any part in the leak, following speculation the government had deliberately set out to discredit him.
But he did not accept that St James's Palace was definitely responsible.
'Farmers persecuted'
The prince was attacked by some Labour MPs and in sections of the media for "meddling" in politics.
But Mr Blair told BBC's Breakfast with Frost: "I have no problem at all with Prince Charles writing to me occasionally, which he does.
"We speak and meet reasonably often.
"I find his views both helpful and informative and I don't have any difficulty with it at all."
He praised the prince's achievement in creating the Prince's Trust charity which helps young people.
And the prime minister said the prince had responsibly highlighted the important issues of organic farming and inter-faith cooperation.
Royal duty
Mr Blair added: "There's no reason why it should stop."
The prince was said to have bombarded the government with letters on issues ranging from "compensation culture" and red tape to political correctness in Britain.
He reportedly relayed countryside campaigners' views they were being treated worse than ethnic minorities or homosexuals.
But a spokeswoman for the prince said it was part of the Royal Family's role to "take an active interest in British life".
And he received support from Environment Minister Michael Meacher and Conservative leader Iain Duncan Smith.