The 51-year-old sister of King Felipe VI is the first Spanish royal to face criminal charges since the monarchy's 1975 restoration, in a case that has sullied the reputation of the royal household and become a symbol of perceived corruption among Spain's elites.
The scandal broke in 2011, just as the country was going through a deep economic crisis.
A court in Palma, on the Mediterranean island of Majorca, is due to rule at noon (11:00 GMT) on whether Cristina and her husband Inaki Urdangarin are guilty. The couple will not be in court for the verdict, which can be appealed.
If convicted, Cristina faces up to eight years in prison for complicity in tax fraud over her 49-year-old husband's work with a non-profit foundation.
Urdangarin, a former Olympic handball medallist who was charged with the more serious crimes of embezzlement, influence peddling, forgery and money laundering, could face more than 19 years in prison and a €980,000 ($1 million) fine over claims he siphoned millions from public funds.
The couple, who have been married since 1997 and have four children together, went on trial last year along with 15 others, including former government minister Jaume Matas.
Urdangarin has grown visibly thinner over five months of hearings that have garnered huge media interest, while the princess has largely stayed mute in court.
The case centres on accusations that Urdangarin used his royal connections to win inflated public contracts to stage sporting and other events, and then siphoned off the proceeds to fund a lavish lifestyle.
He and his former business partner Diego Torres are accused of embezzling about €6 million ($6.4 million) in public money that was paid to the Noos Institute to organise events.
In one example, the company charged authorities €1.2 million for a two-day tourism and sports event -- "a completely disproportionate price" based on a "fictitious budget", according to prosecutors.
Some of the money was allegedly moved to a firm jointly owned by Urdangarin and Cristina, the youngest daughter of former king Juan Carlos I.
Aizoon has been labelled a "front company" in court documents.
Authorities conflicted over whether Cristina should be tried, with an investigating judge insisting she should but the treasury and public prosecutor's office concluding she had not committed any offence.
She was finally tried after a rightwing pressure group, "Manos Limpias" or "Clean Hands", brought a tax evasion case against the princess, as Spanish law permits private groups to initiate criminal proceedings.
But Manos Limpias' own image was tarnished in the trial when its leader was detained for alleged extortion and other charges, accused of asking Cristina's lawyers for money in exchange for dropping its accusations of tax evasion complicity against her.
The scandal exacerbated falling support for Juan Carlos I, who abdicated in June 2014 and handed the crown to his son Felipe.
The current king has publicly distanced himself from his sister, who has been barred from carrying out public functions.
By AFP's Laurence Boutreux