This study integrates the TPACK framework into a Preschool Language Education course to examine its effects on pre-service preschool teachers' instructional design competence (IDC). The research aims to explore effective methods for IDC development and analyze its growth characteristics. Using an R&D methodology, this study employed an experimental design with an experimental group and a control group. Data were collected from 41 pre-service preschool teachers at Putian University, Fujian Province, China, through cluster sampling. The experimental group (n=21) participated in a 13-week TPACK-based course, while the control group (n=20) received traditional instruction. The IDC Scale and Lesson Plan Scoring Rubric were used for data collection. Data analysis included independent and paired t-tests, as well as assessments of lesson plan scores and grade distributions. Key findings indicate that (1) the TPACK-based course encompasses course objectives, content, learning organization, and assessment, with all participants achieving satisfactory or higher lesson plan scores and a 95% satisfaction rate; (2) the course significantly enhances pre-service preschool teachers' IDC; and (3) at the early stage of professional development, IDC growth exhibits characteristics of simplification, linearity, and dogmatism.