This article focuses on the relationship between system design and player experience in role-playing games from the perspective of self-determination theory. In the practical field of game design, there are often gaps between abstract theory and concrete application, and this study focuses on the possible effects of different character progression system designs on the player experience in role-playing games (RPGs) from a practical game design perspective. Four hypotheses were developed based on analyzing three typical games and further tested using questionnaire research and quantitative analysis. Ultimately, a correlation was identified between the consistency of gameplay activities with the purpose of character progression, compulsory repetition, multiple gameplay activity options, and the basic psychological needs of self-determination theory, as well as between basic psychological needs and the harmonious passion of the dualistic model of passion. These basic elements for which correlations exist may be used as specific guides in future game design processes.