Ronaldo is accused of "four crimes against the public treasury between 2011-14... which involves tax fraud of 14,768,897 euros ($16.5m, £12.9m)", Madrid's public prosecutor's office said in a statement.
It continued to say Ronaldo, 32, had used a shell company based in the Virgin Islands to "create a screen in order to hide his total income from Spain's tax office".
He should have paid a tax rate of 24 percent in 2011, and 24.75 percent in the three following years, it said.
The Portugal captain is accused of evading taxes of 14.7m euros (£13m; $16m) from 2011 to 2014.
"This communication, which was not required by law, constitutes irrefutable proof that Cristiano Ronaldo and his representatives are in good faith, and cooperate with the authorities in a spirit of transparency and compliance with legality", the agency Gestifute said.
Speaking to El Chiringuito TV before the Champions League final, Ronaldo said the prospects of being charged is not stressing him.
4 shot, including Louisiana Representative, Texas Congressional staffer
She said the officer had gotten out of a parked vehicle , drawn a handgun and shouted something to the gunman, who then fired. She said he was using a long gun and exchanging fire with law enforcement officers, one of whom yelled for her to get down.
Gestifute, the agency representing the Portugal captain, said in a lengthy statement posted on its website the matter is a complex financial one.
There are of course plenty of similarities with Leo Messi, who has famously had plenty of issues with the tax man in Spain.
Soccer stud Cristiano Ronaldo does not mind taking off his clothes and we are more than fine with that.
Accusations of tax fraud have dogged many of Spain's top players, including Lionel Messi.
Meanwhile Brazil star and Barcelona forward Neymar and his parents are due to stand trial for alleged corruption over his transfer from Santos in 2013.
The 32-year-old Ronaldo, a four-time Ballon d'Or victor, is arguably Europe's leading football player. He led Real Madrid to the Spanish league championship this year and to a successful defense of their Champions League title.
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