With increasing emphasis on enhancing students' communicative competence, oral English skills have become a central focus in English as a Foreign Language (EFL) instruction within Chinese higher education. However, EFL instructors as well as researchers have indicated that most Chinese college graduates lack the ability to communicate effectively in English, and many leave the university with poor speaking skills, which undermines their confidence and capacity to master the language itself. The gap between educational goals and actual outcomes highlights the need to better understand factors that support or inhibit students' willingness to apply English in real-world communication. Therefore, this study aimed to investigate the mediating effect of speaking self-efficacy on the relationship between perceived classroom climate and willingness to communicate (WTC) among EFL students at different types of Chinese universities, including Sino-foreign cooperative universities and traditional domestic universities. Data were collected from 153 undergraduate students at several universities via an online survey. Using regression-based mediation analysis (Process Macro Model 4), the bootstrap analysis of the indirect effect revealed an effect size of 0.29, with a 95% confidence interval from 0.07 to 0.50, which did not include zero, indicating full mediation. Furthermore, multi-group moderation analysis (Process Macro Model 59) revealed that the mediated effect was significant among students from Sino-foreign universities but not those from traditional domestic universities. However, the difference between groups was not statistically significant. These findings highlight the importance of building rapport and supportive classroom environments to strengthen students' speaking self-efficacy and promote greater engagement in oral English communication within EFL contexts.