He could be sentenced to five years in prison and ordered to pay a fine of 4 million euros ($4.5 million), in addition to the amount allegedly defrauded.
The Juventus forward, who played for Real Madrid from 2009 to 2018, agreed to settle the case by paying an €18.8m fine and accepting a suspended jail sentence.
The Portuguese star, who was a stalwart in Real Madrid's attacking formation between 2009-14, moved to the Serie A club Juventus over the summer.
Ronaldo had to enter the courtroom through the front door after his request for special security measures to avoid the spotlight was denied on Monday.
Dressed in black and wearing dark sunglasses, a smiling Ronaldo climbed up the courthouse steps holding hands with his girlfriend Georgina Rodriguez.
A court spokesman said it was not immediately clear if this fine would be added onto the 18.8 million euros that Ronaldo had agreed to pay Spain's taxman under a deal reached in June previous year.
Prosecutors accused him of four counts of tax fraud from 2011-14 worth 14.7m euros (£12.9m) and using shell companies outside Spain to hide around 28.4m euros (£25m) made from image rights.
Cristiano Ronaldo was back in Madrid on Tuesday morning as he attended a court date for his tax case.
Real Madrid's Marcelo Vieira admitted to tax fraud and accepted a four-month suspended jail sentence over his use of foreign firms to handle nearly half a million euros in earnings.
Ronaldo has always denied the accusations.
Other players that have had to do deals with the Spanish courts over tax fraud include Luka Modric, Marcelo, Radamel Falcao, Ángel Di María and Javier Mascherano.
Between 2005 and 2010, foreign players in Spain were protected under the so-called "Beckham law" allowing them to curb their taxes.