In major emergencies, emergency voluntary organizations play an important role as the main body of auxiliary rescue. This study selected H volunteer organization in epidemic relief as the research object, focused on “the operational mechanism of emergency volunteer organizations in major emergencies and the logical relationship among various elements”, conducted exploratory single case study, and constructed the operational mechanism model of “mission-driven---network connection---resource allocation”. It is found that organizational mission is the key factor driving the efficient operation of emergency voluntary organizations, the evolution of network connection structure is an important factor for the efficient operation of organizations at the structural level, and provides a basic guarantee for resource allocation, and different ways of resource allocation are important ways for the efficient operation of organizations at the action level. In the initial construction period, the mission of emergency voluntary organizations germinated and trust was quickly established. The organizations were connected by a star-shaped network structure and used existing interpersonal relationships to allocate resources. During the adjustment period, the mission is strengthened, and the collaboration and cooperation in the early stage promote knowledge sharing. The organization connects with the chain network structure, and allocates resources with knowledge, experience and other expertise. In the stable period, the mission is internalized in the heart, and the organization has a high degree of identity. The organization is connected with the ring network structure, and resources can be actively pooled through the role of reputation and trust.This paper explores the efficient operation mechanism of emergency voluntary organizations from the dynamic perspective of organization level, which has enlightenment significance for the improvement of operation efficiency of emergency voluntary organizations in major emergencies.