Many studies have confirmed that digital game-based learning can effectively improve students' learning motivation and that properly integrating learning strategies into digital games can effectively improve students' learning achievement. However, rare research has been considered the long-term effect of learning retention. In the current study, a game-based learning system that integrated a "Prediction-Observation-Explanation" learning strategy was developed to provide learners with appropriate guidance and feedback during the learning process to improve the learning retention. A quasi-experiment was conducted in an elementary school mathematics course to evaluate the effectiveness of the method. The experimental result shows that the proposed approach can significantly improve students' learning achievement and learning retention. According to the analysis of students' behavioral pattern, the proposed approach can help students focus on the learning material of the game. Therefore, the proposed approach is a potential and effective way to help students with better long-term learning performance.