Coproduction has been widely advocated for, but there are theoretical and empirical disagreements as to whether trust in government can encourage coproduction. This study proposed external and internal efficacy as potential moderators to further understand this relationship. We designed a questionnaire with 537 citizens, and a 2 × 2 × 2 between subjects survey experiment with 375 citizens to test our hypotheses in four urban governance scenarios in China. The findings provide solid empirical evidence for theoretical disagreements about coproduction and new ideas for mobilizing it.