Adrian Ursache, 42, is accused of shooting one policeman in the throat in August 2016, when he opened fire on a special unit sent to evict him from his home in the village of Reuden.
An armoured vest saved the police officer's life, while Ursache himself was badly hurt in the firefight.
He could face a life sentence if found guilty.
As the trial got under way under heavy security, Ursache's lawyers immediately demanded it be called off, claiming the charge documents were incomplete and riddled with errors.
"I was holding a weapon in my hand, but I didn't fire at any moment" during the confrontation with police, the accused told a journalist in the courtroom before proceedings began, adding that he only "resisted" the officers.
Ursache won the "Mr Germany" contest in 1998, going on to marry a former
beauty queen and have two children.
The country's internal security services suspect he belongs to the shadowy "Reichsbürger" or "citizens of the Reich" movement, an umbrella term for disparate groups that reject the modern Federal Republic of Germany.
Reichsbürger followers generally believe in the continued existence of the pre-war German Reich and several groups have declared their own states.
Many refuse to pay taxes, social contributions or fines and issue their own identity documents, practices that bring them into conflict regularly with state authorities.
Neo-Nazi views and conspiracy theories are widespread among adherents of the movement.
Ursache's gun battle with police launched a series of violent confrontations involving so-called "Reichsbürger".
Another follower, Wolfgang Plan, appeared in court in Nuremberg in late August accused of shooting a policeman dead during an October 2016 raid.