While flipped learning has attempted to explain the benefits of technology applied to educational settings, this study aims to validate research questions and test the theory of the learning strategies in flipped learning. A self-designed questionnaire, consisting of 17 critical indicators of online self-regulation, project-based learning and 5-competence development, was administered to collect data from 87 college students in China. The partial least squares structural equation modeling (PLS-SEM) was used to analyze the relative factors. The results indicated that an integrated model, combining online self-regulation and project-based learning, provided a marginally better explanatory power; project-based learning had a better prediction of 5-competence development than online self-regulation. An integrated model is proposed to detect the latent relationships among the data with structural equation modeling (SEM). The SEM provides a clear picture of the relations among the variables, and shows that online "Help seeking" in MOOC lecture videos and engagement in "Teamwork" in class are the key indicators of student engagement in flipped learning. This study adopted an innovative approach which emphasizes the diagnosis of students' engagement, and proposes an integrated model combining online self-regulation and project-based learning constructs for a theoretical framework to predict learning performance in flipped learning.