WASHINGTON — “Wonder Woman,” the 2017 film that Steven Mnuchin helped produce before becoming Treasury secretary, hauled in about $90 million at the box office in China. It was the film’s most successful international market and a roaring success for an American superhero export. But because of China’s strict laws for foreign films, the studio behind the movie, Warner Bros., received just a small fraction of those revenues.

Now, as Treasury secretary and one of the lead negotiators in trade talks with China, Mr. Mnuchin has been personally pushing Beijing to give the American film industry greater access to its markets — a change that could be highly lucrative to his former industry. While Mr. Mnuchin divested from his Hollywood film production company after joining the Trump administration, he maintains ties to the industry through his wife, the actress and filmmaker Louise Linton.

In 2017, Mr. Mnuchin sold his interest in the company, StormChaser Partners, to Ms. Linton, who at the time was his fiancée. In his 2018 disclosure, which was obtained from the Treasury Department through a records request by The New York Times, StormChaser is listed as one of Ms. Linton’s assets.

Since they are now married, government ethics rules consider the asset to be owned by Mr. Mnuchin. And while the documents show that Mr. Mnuchin sold his stake to Ms. Linton for $1 million to $2 million, he is now owed that same amount, in addition to interest, from StormChaser in 2026, according to the 2018 form.