Increasing demand for various social services in accordance with the global social change in time requires a systematic and efficient system based on a user-oriented policy operation method beyond an administrative operation method of social services. Therefore, this study aimed to present a specific direction for the development of the social service system by empirically deriving and discussing the critical factors that can lead to sustainable success of the social service system. To this end, 12 factors in 3 areas were critically analyzed through a questionnaire survey and analysis on the basis of the Analytic Hierarchy Process (AHP) method for the social service workers and users of the 50 Plus Foundation, an organization that helps the elderly in Seoul to continue their social participation. The analysis results confirmed that the service delivery system was the most important factor among the service delivery system, service administration, and service network, and, in particular, factors for users’ active system access, such as accessibility and participation possibility, were the most influential factors for sustainable success of the social service system. Ultimately, unlike in the past, system development and direction should be sought by considering service users rather than a one-sided policy approach of the government for the development and operation of the social service system.