Expectation Horizon is an important concept in the study of Receptional Aesthetic. Translation of Idioms shall be faithful to the culture of source language and meet the expectation of target readers to realize the communication of culture. This paper argues that the reception of the target text is restricted by and broadens target readers' existing expectation horizon. The gap between target readers' existing expectation horizon and the text shall be bridged by readers' creative expectation. In translating idioms, translators shall understand fully receptor's expectation horizon and satisfy reader's creative expectation to accomplish translation equivalence.