Students of Southeast Asian Heritage Learning Chinese (SSAHLC) in Taiwan have frequently demonstrated difficulty with traditional Chinese (a graphical character) radical recognition due to their limited exposure to the written language form since childhood. In this study, we designed a Chinese radical learning game (CRLG), which adopted a drill and practice mode, for SSAHLC to practice recognizing Chinese radicals. To facilitate Chinese writing, non-native learners need to use aspects of the radical knowledge as cues to encode characters, from which the contents of the game were built up for SSAHLC to master the Chinese written forms by playing the CRLG with gesture-based interactions. In addition, the game was used to explore the students' intrinsic motivation relevant to online learning self-efficacy, as well as the experience of flow, to predict the degree of learning progress. Data were collected from 78 SSAHLC participating in the study, and 73 valid questionnaires were returned. After applying confirmatory factor analysis as well as structural equation modeling to the valid data, it was found that four constructs, namely intrinsic motivation, online learning self-efficacy, flow experience, and learning progress, were all positively correlated. Our results indicated that intrinsic motivation of Chinese learning predicted online learning self-efficacy, and that flow experience was relevant to the students' learning progress. Moreover, the degree of learning progress could be predicted by the mediating factors. These findings imply that heritage language teachers may utilize the CRLG to enhance learners' Chinese radical recognition ability, and eventually improve their Chinese character recognition ability.