Project-based learning using online learning environments is becoming increasingly popular. To in-depth explore the behavioural patterns and limitations faced by students in project-based learning where online forums are used. This study conducted an empirical case study of an online project-based learning activity in a management course, in which 70 college students participated. The study integrates two analytical approaches: quantitative content analysis and progressive sequential analysis. The analytical approaches allow researchers to explore and visualize the content and patterns of participants' online project learning discussion behaviours. The results indicate that learners' limitations include poor time-management and insufficient initial data collection. The students also demonstrated a lack of proper data evaluation processes and sufficient comprehensive analysis. The limitations are in-depth discussed and suggestions for teachers and educational software developers are also proposed. (Contains 4 figures and 3 tables.)