Translanguaging, a practice that integrates a first language (L1) and a second language (L2), has gained attention in English as a Foreign Language (EFL) teaching for its potential to facilitate communication and learning. Although translanguaging is increasingly studied, research specifically examining its impact in EFL practicum settings remains limited. This mixed-methods study investigates how English language proficiency (ELP) influences the translanguaging practices of 180 Chinese EFL preservice teachers during their practicum at a central China university. Quantitative data were collected using the TOEFL Independent Speaking Rubric to assess ELP and a translanguaging questionnaire to measure translanguaging frequency. Qualitative data were gathered through interviews and classroom observations. Quantitative analysis explored correlations between ELP and translanguaging frequency, while qualitative data were analysed thematically to understand how ELP shapes translanguaging practices. The findings suggest a positive correlation between ELP and translanguaging practices. Specifically, preservice teachers with higher ELP use translanguaging more frequently, particularly for explaining complex content in L1, supporting language proficiency in L2, and creating an inclusive classroom environment. The findings imply that enhancing ELP among Chinese preservice teachers could be instrumental in promoting effective translanguaging practices within EFL classrooms. This study highlights the need to prioritise ELP development in EFL practicum programs. The findings could inform EFL teaching reforms and further the integration of translanguaging in EFL education.