The research on efficiency of medical service is of great significance since medical service is a nationwide concern. The study attempts to apply the chance constrained DEA model to evaluate the regional efficiencies of medical service for 31 Chinese provinces in 2006 and analyze some possible reasons for low efficiency in some specific provinces. Furthermore, the study obtains the ideal output value in 2007 with the output-oriented analysis based on both non-increasing and proportionally-increasing inputs conditions. Finally some constructive suggestions are provided based on the results.