Although flipped learning has been recognized as being a potential approach enabling students to learn at their own pace before the class and facilitating in-depth peer-to-peer and student-to-teacher interactions in the class, it remains a challenge to promote students' active learning in the before-class stage, which could significantly affect their in-class engagement and learning performance. In this study, a reflective thinking-promoting approach is proposed to facilitate students' learning design project performance, technology-enhanced active engagement, and their reflective thinking and participation in the before-class stage of flipped learning. A quasi-experiment was conducted on a flipped Digital Learning course of a Master's program in a university to evaluate the effects of the approach on students' learning design performance, engagement, reflective thinking and participation. A total of 19 students (7 male and 12 female) were in the experimental group learning with the reflective thinking-promoting approach, while 19 (4 male and 15 female) were in the control group learning with the conventional flipped learning approach. The results indicated that the proposed approach significantly enhanced not only the students' learning design project outcomes and reflective thinking, but also their engagement and participation in the before-class stage of flipped learning.