The Deliverance star was ordered to pay actress Anderson $4,000 (£2,670)-a-month to help raise their adopted son Quinton when they divorced in 1993 after five years of marriage.
But Reynolds allegedly failed to keep on top of his financial responsibilities and would send his ex a cheque every few months.
According to the National Enquirer, he has now racked up a debt of $400,000 with Anderson - but she has decided to write off the amount following his recent health struggles.
The actor underwent major heart surgery earlier this year (10) after he was diagnosed with clogged arteries, months after completing a stint in rehab for alleged addictions to prescription drugs and alcohol.
And Anderson - who has since wed her high school sweetheart, folk singer Bob Flick - is said to have wiped the debt out of sympathy for the star.
She has reportedly told pals, "I feel sorry for Burt. I'm not going to pursue it anymore. I don't want to call him a deadbeat bad on top of all his other troubles.
"I almost feel guilty for being so happy, and with Burt so vulnerable I don't want to end up looking like the bad guy."
A source adds, "Loni could use the money Burt owes her. She isn't working much, but she's decided not to go after him any longer."
The former couple's son, aspiring DJ Quinton, is now 21 and studies at a technical school in California.