Abstract: Online public opinion on major medical accident has many significant characteristics, such as a tremendous participation group, opinions that can hardly settle down in a short time and highly social heat. Ordering control research of online public opinion is meaningful during the process of major medical accidents public crisis management. This paper chooses the case of Xiangtan maternal to do the empirical research from the perspective of dissipative structure theory. After analysis of evolution of public opinion using text mining and social network method, five measures are proposed, involving maintaining the openness of the system, ensuring the original state of the system to be non-equilibrium, making full use of the nonlinear restrictive relation between elements, guiding the direction of public opinion in the light of the general trend, and establishing the perfect online public opinion early warning mechanism.

Key words: Major medical accidents, 　Online public opinion, 　Ordering control, 　Dissipative structure theory, 　Text mining, 　Social network analysis