In the context of population ageing, the number of elderly patients with dementia is increasing day by day. This disease seriously affects the quality of life of the elderly and causes huge burdens and pressures on families and society. At this stage, issues such as low level of attention at the national and social levels, weak ability of active screening and identification, high treatment and care costs, and fragmented social service system are prominent in the elderly dementia. It is imperative to actively explore the construction of a care system that covers the entire life cycle of dementia in the elderly, which is composed of multiple welfare subjects such as the government, community, family, market, and civil society organizations. Based on the practice of the full-cycle support project for elderly patients with dementia and their families in Beijing X Hospital, the research takes the theory of welfare pluralism as the framework, and constructs the implementation path and mechanism of the welfare pluralism care system for the elderly with dementia through action research. Based on the portrayal of the reality of the elderly with dementia, health social workers break through the shortcomings of the original medical social work service, such as the single service object, the confinement of the service place, the disconnection of the needs of patients with different disease cycles, and the poor effect of the resource link, etc., turn to the perspective of health social work to use the method of action research to try to break the situation from four directions: in the stage of early detection of dementia, we can clarify the responsibilities of service subjects and maximize service effectiveness; in the stage of early treatment of dementia, we can break down barriers between service subjects and realize the value of resources flow; in the stage of self-management of patients with dementia, we can mobilize the subjective initiative of service subjects to achieve positive transformation of target group; in the dementia friendly advocacy stage, we can respond to the internal needs of service subjects and achieve sustainable development of the care system.