Francis said proselytizing isn't his style — in politics or religion.
Speaking to reporters while traveling home Saturday from a trip to Portugal, Francis said he would say what he thinks sincerely to Trump and listen respectfully to what Trump has to say.
"I never make a judgment about a person without hearing him out," the pope said.
Speculation has swirled about what Trump and Francis will discuss during their May 24 audience, given Francis has already said anyone who wants to build walls to keep out migrants is "not Christian."
Trump, who made building a wall along the border with Mexico a signature campaign promise, responded by saying it was "disgraceful" that the pope would question his faith.
Francis said that in talks, he always tries to find "doors that are at least a little bit open" where common ground can be found, particularly in peace-building.
"Peace is artisanal. You do it every day," he said.
Asked specifically if he would try to soften Trump's policies, Francis said: "That is a political calculation that I don't allow myself to make. Also in the religious sphere: I don't proselytize."
Trump will call on Francis mid-way through his first foreign trip, after visiting Saudi Arabia and Israel and before attending a NATO summit in Brussels and a G-7 summit in Italy.