What is equivalent of "分润"?
Sort of.

The the generic 分润 just means "profit-sharing", which is also an easily understood, and similarly generic, English term. Alternatively, "a cut of the profit" would also be widely understood, but obviously that's not a single word.

You might also be able to use the English term "fee-splitting", if you're talking about sharing fees with a referrer for referring a client (typically, doctors or lawyers). In situations of a illegal connotation, the term "rake-off" could be used. Similarly, the term "kickback" could be used, but illegality/coercion tends to be implied with that as well.

If you insist on a single word, the generic profit sharing meaning has a word borrowed from French: tantième. I doubt it's a term with much currency in real life, however.