In this paper, a theoretical method for the calculation of the glossiness of waterborne paint with high gloss was reported. The theoretical glossiness of the waterborne coatings was calculated from the specular reflectance R of the coatings by Fresnel formula based on the refractive index of various materials. The theoretical calculation method has been verified by a large number of practical samples. The results showed that the refractive index of waterborne paint was additive if the resin had good compatibility. As long as the surface of the paint film was smooth and flat, the calculated value of the glossiness at 20 degrees and 60 degrees was very consistent with the measured value. It can provide a good theoretical guidance for the design of waterborne paint products with high gloss and high fullness in paint coatings industry, especially in automobile industry.