Previous research indicated that service learning (SL) is an effective pedagogy to improve students' problem-solving ability and increase their classroom engagement. However, studies on SL are rare in China. This study examined the effects of SL on the problem solving of Chinese undergraduate students as well as the mechanism through which it worked. Eighty-two students were divided into two groups: the SL group participated in a SL activity during whole semester and the contrast group (no-SL group) underwent other comparable learning tasks. The study revealed the differentiated effects of SL on students solving different types of problems and investigated the mediating role of classroom behavior engagement in problem solving. The research findings suggested that teachers should provide students with authentic and ill-structured problems to increase their classroom engagement as well as far transfer.