Based on the contingent valuation method (CVM), maintenance service values of the ecosystem diversity of marine protected areas and the diversity of important marine species in Sanya coastal waters were evaluated. The questionnaires were administered face-to-face to survey the willingness to pay (WTP) of local urban residents to maintain the sustainable existence of the diversity of marine protected areas and important marine species in Sanya coastal waters in December 2014. The multiple linear regression equation model of WTP was set up and extended to the whole urban residents of Hainan province. Meanwhile, in the case study, problems related to the CVM such as design and survey techniques of the questionnaires, deviation analysis, reliability, and validity testing of the results were also resolved. The results showed that:(1) total maintenance service values of ecosystem diversity of marine protected areas and the diversity of important marine species are 373.4 million CNY and 444.2 million CNY, respectively; (2) socio-economic variables of the respondents such as education degree and annual income per person significantly influenced the values of the WTP of the respondents, which is consistent with the economic theory; (3) as a kind of evaluation method to state the preferential value, the result of CVM is greatly influenced by the deviation. In order to minimize the deviation, the design and survey techniques of the questionnaires need to be strictly controlled; and (4) the design of the payment amount in CVM study has well defined the range and distribution of the respondents' WTP, which makes the statistical efficiency of the value of the WTP to be relatively higher than expected. The reliability of the CVM has been verified, which testifies the validity of the CVM justified in the non-use value evaluation process of ecosystem services. Given that it is difficult to advance in terms of education degree and income of local urban residents in a short time, it is suggested that the relevant marine administrative departments should strengthen the publicity and education activities of marine protected areas and marine biodiversity in Sanya coastal waters to improve the cognition and protection consciousness toward them.