Ronaldo is accused or "four crimes against the Public Treasury between 2011 and 2014, which involves tax fraud of 14,768,897 euros ($16.5 million)", the Public Prosecutor said in a statement, reports Xinhua news agency.
Ronaldo is said to have taken "advantage of a company structure created in 2010 to hide income generated in Spain from his image rights from tax authorities in a 'voluntary' and 'conscious' breach of his fiscal obligations in Spain," according to the Prosecutor's Office.
The 32-year-old, considered by Forbes magazine to be the highest paid athlete in the world, is thought to have set up companies in the British Virgin Islands and Ireland in order to channel off his earnings.
Ronaldo is the latest in a line of footballers to have problems with Spanish tax authorities, with Lionel Messi the highest profile player to be affected.
The Barcelona star was sentenced to 21 months in jail after being found guilty of avoiding taxes on 4.16 million euros ($4.66 million) of image rights during the period 2007-2009. Ronaldo is accused of defrauding over three times more money than Messi.
Other players to be accused of tax fraud include Fabio Coentrao, Falcao and Pepe, all of share the same agent (Jorge Mendes) as Ronaldo.