After Ms Wang died in 2007, Peter Chan, formerly known as Tony Chan, claimed he was the sole beneficiary of her estimated $4bn (Â£2.6bn) estate.
The case of the eccentric billionaire widow and her alleged geomancer lover transfixed Hong Kong.
A court ruled two years ago that her estate would go to charity.
The BBC's Juliana Liu in Hong Kong reports that during the trial the  jurors heard many lurid and colourful stories about the unlikely couple.
They were told, for example, that Chan first wooed Nina Wang, who was then one of Asia's richest women, with a head massage.
When sentencing Chan, Justice Andrew Macrae spoke of the "shameless and unparalleled greed" at the heart of a "well-executed and well-planned" crime, Reuters news agency reports.
"Never once ... have you shown the slightest remorse for your conduct," he is quoted as saying.
Chan, who had pleaded not guilty on charges of forgery and using a forged document, was impassive during the sentencing, Reuters reports.
The self-styled Feng Shui practitioner changed his name from Tony Chan to Peter Chan earlier this year after he converted to Christianity.
Chan fought for years to inherit the property tycoon's multi-billion dollar fortune, claiming he was the sole beneficiary according to a 2006 will.
But a court finally dismissed his claims to the inheritance in 2011, ruling in favour of a charity run by Ms Wang's siblings, Chinachem Charitable Foundation Ltd, whose claim to her estate rests on a will from 2002.
Ms Wang, who was 69 when she passed away, was known for her pig-tails, short skirts and colourful dress sense.
She was the widow of Hong Kong industrialist Teddy Wang, who disappeared in 1990 after being kidnapped.
A court in Hong Kong has sentenced a Feng Shui master to 12 years in jail for forging the will of billionaire tycoon Nina Wang.