"By the end of this month, the Chinese side will submit to the UN secretariat on climate change our intended nationally determined contribution," Li told a press conference after a summit in Brussels with EU leaders Donald Tusk and Jean-Claude Juncker.
There has been speculation that the announcement would be made during Li's visit this week to Brussels and Paris, where December's climate talks will be held.
Li starts an official visit to France on Tuesday, the last day of the month,
Li added after signing an agreement with the EU on the issue: "We are willing to work together with the EU side to jointly tackle the challenges of climate change."
All countries are meant to propose their targets for cutting emissions ahead of the UN-led talks which are aimed at forging a pact to limit global warming to two degrees Celsius (3.6 degrees Fahrenheit) over pre-industrial revolution levels, to take effect from 2020.