WASHINGTON—Chinese Finance Minister Lou Jiwei called GOP presidential front-runner Donald Trump an “irrational type” and said the U.S. “wouldn’t be entitled to world leadership” if it followed Mr. Trump’s proposed trade policies toward China.

Mr. Trump has advocated imposing up to 45% tariffs on China as a way to force it to change its trade policies. Mr. Lou, known in China for his outspokenness, said in an interview with The Wall Street Journal that such a tariff would violate World Trade Organization rules. Under those...