Christie McCarthy's life has come full circle in the wildest way imaginable ... she tells TMZ she was abandoned in a box as a newborn in China -- and now she's making a fortune showing off her own on OnlyFans!

The influencer -- aka Christie McFit -- tells us her story began during China's One-Child Policy, when she was left in a box outside a police station before eventually being adopted and raised by a single mom in suburban New Jersey.

Fast-forward a few decades ... Christie now boasts more than 2.5 million Instagram followers, says she's in the top 0.07% of all OnlyFans creators, and has traded her hard life as a baby for first-class flights, luxury vacations, and what she calls her dream life.

It wasn't always that glamorous. Christie tells TMZ she grew up ashamed of her Asian heritage, even trying to distance herself from other Asian students ... while relentless teasing over her "flat ass" became her biggest insecurity.

Christie says she doubled down on herself with two BBLs -- calling them the best investments she ever made as her OnlyFans career took off.

From abandonment to abundance ... Christie says she's living proof your beginning doesn't define your ending ... "all thanks to the people who support me online."

She took one box ... and built an empire with another!