Eyes are a critical part of facial expressions. Because of the appearance diversity of eyes due to motion, it is difficult to synthesize eye with a particular facial expression. Traditional methods have failed to adequately catch motion-related appearance changes. In order to generate a photorealistic expression eye, we propose a two-step method. Firstly, we propose an eye curve model to represent the eye. The model uses one circle and four skewed elliptical arcs to represent the shape of eyes, and divides the entire eye region into 6 sub-regions that correspond to different anatomical components of the eye. Then we propose a structure-based similarity (SBS) framework to synthesize the expression eye using the eye curve model. This paper primarily contributes three things: First, the proposed eye curve model can represent the diversity of eyes, which is better than some traditional models. Second, when there are many samples, our method can synthesize expression eyes with personal style, which is more reasonable when synthesizing common expressions such as joy. Third, when there is only one sample, our method can clone this expression, which is more useful when synthesizing very special expressions such as a grimace. Experimental results show that all synthesized eyes are realistic and expressive.