Mental calculation is an important and fundamental skill. The performance of mental calculation can gain considerable improvement through extensive practice. However, extensive practice usually makes students bored. Digital game was suggested as a good element to enhance students' motivation to learn. Therefore, turning extensive mental calculation practice into game is potentially a good way to engage student in extensive practice. Four mini games were designed in this study as the extensive practice environment. Students' performances were analyzed based on high, mid, and low achievement levels. The results were discussed in five aspects: (1) accuracy; (2) response time; (3) time on task; (4) motivation; (5) engagement. Generally speaking, we receive positive result on all five aspects, but there were some differences among different achievement level students. Further studies are needed to solve these problems.