Atmospheric refractive index structure parameter ( C2n ) is one of the impotant physical quantities measuring the degree of turbulence. The refractive index structure parameter under the sea surface environment in Yantai region from January to June in 2014 is measured by using a large aperture scintillometer. The statistical properties of measured data are analyzed, including frequency count, daily variation and monthly variation. The change characteristics of C2n under the sea surface are compared with other environments. The comparative analysis result reveals that the value of C2n varies between 10-17 m-2/3 to 10-14 m-2/3 under the sea surface environment, which is classified as medium and weak turbulence. The C2n at different times are not presented the variable characteristics of“conversion time”, and there are no significant differences between C2n in the daytime and C2n at night. The daily mean vary between 10- 16 m-2/3 to 10- 14 m-2/3 . At the same time, the discrete degree of C2n is analyzed combing standard deviation.