"The performance forecast correction is the result of preliminary estimate by company's financial department," Beingmate said.
Details of the loss will be revealed when the company releases its annual report in March.
Fonterra's chief financial officer, Lukas Paravicini, said that Beingmate's recent performance reflected China's market conditions, "which remain challenging for all dairy players".
"The long-term outlook remains strong with disposable incomes in China growing by 11.5 per cent a year since 2006, the relaxation of the one child policy taking effect and tightening brand regulations leading to the exit of many smaller competitors from the marketplace," Paravicini said in a statement.
"We are confident in our overall China strategy, of which our Beingmate partnership continues to be an important part," he said.
"Our partnership with Beingmate is a long-term investment to grow in the domestic infant formula market," he said.
"It also supports future ingredient sales of our NZMP brand from New Zealand, and our whey products from Australia and Europe."
Distribution of Fonterra's Anmum infant formula brand in China has grown from 60 cities in 2015 to more than 170 cities today.
Total sales were also ahead of projection, he said.
Fonterra said it would update farmer shareholders Beingmate when the co-op releases its first half result in late March.