Hugh Hefner's famous last name isn't doing much good these days for his widow Crystal ... and now that she's written a book about their marriage, she's done with the Hefner name.

Crystal says she doesn't want to be a Hefner anymore... and feels she needs to change her name back to what it was before she met the Playboy founder ... Crystal Harris.

Hugh's 3rd and final wife was on Rachel Uchitel's podcast Miss Understood when Rachel asked Crystal if the Hefner name helped her or hurt her.

Crystal, who was married to Hugh when he died in 2017, says Hef's secretary quickly changed her last name to his after their 2012 marriage ... telling Rachel it was all done at Hugh's behest. Crystal says she really had no involvement in the process.

It wasn't until Crystal started writing her new memoir, "Only Say Good Things: Surviving Playboy and Finding Myself," that she says she started thinking about how she felt about being a Hefner.

Now that she's shared her story -- taking shots at Hef, the Playboy Mansion and his company in the process -- Crystal says she's ready to legally change her name back to Harris, permanently closing the book on the Hefner chapter of her life.