The prosecutor's office in Madrid says it has filed a lawsuit against the Portuguese player.
He is accused of evading tax of 14.7m euros (£13m; $16m) from 2011 to 2014.
The world's highest-paid sports star had previously said he was not worried about tax investigations as he had nothing to hide.
On this occasion he is accused of knowingly using a "business structure" to hide income made from his image rights.
In December, leaked documents suggested that Ronaldo had avoided tax on income allegedly held in offshore accounts.
He denied the allegations.
When asked about that investigation, he told a journalist from Radio Television Portuguesa (RTP) "Quien no debe no teme", which roughly translates as "He who has nothing to hide has no fear."