Background: During the COVID-19 pandemic, online collaborative problem solving (online CPS) has become one of the most crucial learning methods to develop students' learning performance. However, it remains unclear of the effectiveness of the online CPS method on students' learning performance. Objectives: To explore the overall effect of online CPS methods on students' learning performance and identify the moderating factors that influence this impact, we employed a meta-analysis approach to analyse the combined effects of 31 articles. Results: The results showed that the online CPS method had a medium impact on students' learning performance, with an overall effect size of 0.526. The moderator analysis indicated that the online CPS method was more effective for: (1) college preparatory learners; (2) the discipline of Economics; (3) grouping method of assigned; (4) teacher-led instruction; (5) study duration of 2 to 4 weeks; (6) group size of 3-5 members; (7) synchronous online environment; and (8) cognitive performance. Implications: Based on these findings, we recommend using the online CPS to improve students' cognitive and affective learning performance. To enhance students' social learning performance, instructors should design reasonably to use collaborative scaffolding to engage students purposefully and constructively in online CPS activities.