The work aims to use a multilevel service design process and methodology to create a digital therapeutics (DTx) service system that can satisfy youth groups' needs for digital mental health interventions, based on the principle of value co-creation. By going over the history of DTx through a literature review, theoretical underpinnings and practical applications of value co-creation and multilevel service design were explained. The five-stage multilevel service design process was then used to finish the design of the DTx service system. Value co-creation served as a theoretical roadmap for optimizing the DTx service solutions' value creation mode, value delivery method, and resource utilization efficiency at three different levels:service concept, service system, and service encounter. This article presented four design strategies that could be used to drive the design of DTx service systems and generate a DTx service solution with high usability, user satisfaction, and user experience levels after design practice and usability testing. DTx is an emerging digital mental health intervention that can offer patients with a new digital healthcare service experience. In particular, offering patients with a DTx service solution that satisfies their value demands and has a positive user experience can help to improve patients' therapeutic engagement and compliance.