The Contingent Valuation Method (CVM) is one of the most widely used methods to assess the values of natural resources and environmental goods. Through questionnaires, CVM induces people's preferences and makes an expression of monetization; the induced value of Willingness to Pay (WTP) is based on a hypothetical market. The inducing technique or the questionnaire format used to derive the maximum WTP is an important subject among CVM research. A great variety of questionnaire formats have been developed and applied in practice, among which the Dichotomous Choice CVM is considered one of the most advanced methods nowadays. The open-ended double-bounded Dichotomous Choice questionnaire, which is universally applied in foreign literature, combines the advantages of Dichotomous Choice and open-ended questionnaire. It induces the respondents' true WTP, reduces the deviation of assessment results, and thus makes the statistics results more accurate and reliable. In this study, with the open-ended double-bounded Dichotomous Choice CVM, we looked into the respondents' WTP mainly based on the interview survey and supplemented by the online survey, aiming to evaluate the ecological conservation value of Sanjiang Plain Wetland and the respondents' WTP to protect Sanjiang Plain Wetland ecology, and identify what factors influence their WTP. It is important to analyze what factors influence WTP in the related empirical studies. Researchers are continually attempting to expend the influential factors reflected by CVM. The spatial distance factor has now been gradually incorporated into the influential mechanism research of WTP in CVM. The respondents' WTP and the distance between respondents and environmental resource that serves as the evaluation object has a negative relationship, that is, the WTP of the respondents is relatively lower if they are further away from the evaluation object. This phenomenon is called the "Distance Decay Effect". The distance factor is defined as the straight-line distance between the respondents and evaluation object, and incorporated into the WTP Function Model as an independent variable along with other personal, social and economic attribute variables to verify that the willingness has the characteristic of "distance decay". The Dichotomous Choice CVM was used to evaluate the ecological conservation value of Sanjiang Plain Wetland. The WTP Function Model was applied to build the Double-bounded Dichotomous Choice CVM Data Analysis Model, and the parameter regression model of survival analysis was used to establish the influential factor analysis model of WTP. The conclusions are shown as follows: (1) in 2010, the WTP to protect Sanjiang Plain Wetland is RMB 134.582 per person, and the total ecological conservation value of Sanjiang Plain Wetland is RMB 3.3412 billion per year; (2) some factors have significant effects on the WTP, such as respondents' gender, age, educational level and personal annual income. The WTP is higher among people with higher education and income, while it is lower with the aggrandizing of age and distance. Besides, the WTP of female is significantly higher than that of male. The findings will provide useful references for government to make related ecological policies.