Artificial intelligence (AI) is useful to English as a foreign language (EFL) learners, but there is a paucity of research on how they perceive AI. Contextualized in a Chinese university setting, this study investigated Chinese university EFL learners' perceptions of Grammarly in English writing. Based on an extended technology acceptance model (TAM) with task relevance, subjective norm, and perceived enjoyment being added, quantitative data were collected from 140 Chinese EFL learners. Structural equation modeling analysis suggested that the proposed model could effectively explain participants' views of Grammarly. Their perceptions of ease of use significantly influenced usefulness, which had a major impact on their attitudes towards AI and behavioral intention. Perceived enjoyment and task relevance were also significant predictors of students' perceptions of this software. The research model explained 71% of the variance of EFL learners' intentions to use AI. Suggestions were given to teachers on implementing AI writing support.