At present, China is growing to be one of the biggest and fastest economies of the world and Chinese cities actually have accounted for most of the growth. With the rapid development of Chinese cities, more and more rural migrants crowd into cities and bring about various urban development issues related with housing, work, transit, and medical care etc. The ecological vulnerable groups, mainly the rural migrants and the urban low-income, in turn, response to these coupled changes through their daily living activities like medical care that this study focus on. Their medical behaviors can be looked on as the positive feedback to external influences. Accordingly, this paper aims to disclose the ecological vulnerable groups' medical treatment preference and decision, taking Xi'an as a case, which is a rapid growing city with a long history in China and a big population in northwestern China. Based on data from random questionnaires and deep interviews on the ecological vulnerable groups in Xi'an collected during the summer of the year 2011, regression model of Logistic is established from the ecological vulnerable groups' attributes and social factors. Among all the social factors, there is an obvious linear relationship between satisfactory degree for medical service, superiority or inferiority of medical conditions and complexity of the medical procedures with the ecological vulnerable groups' medical decision-making behavior. Finally, two types of medical behavior patterns are defined as the "autotrophic" and the "heterotrophic", which are concepts learned from ecology.