As a commonly used service design process, the Double Diamond Model needs to focus on the problems discovered in the early stage of definition, which requires a high level of experience and ability from designers. The work aims to explore whether there are tools that can help designers more accurately complete service definition, thereby better guiding the subsequent design. The value proposition design was introduced into the Double Diamond process and a service design "Bow-tie Model" was proposed. The process of value proposition design was demonstrated through a case study of "CHUNSHU" community health and wellness service design focusing on social welfare. The "Bow-tie Model" with value proposition design process can help designers focus on problems and establish design directions more effectively, thereby reducing uncertainty in the development and iteration stages of the service design process.