Abstract: The imaging principle of arrows and hearts effect of diamond is studied.The hearts are the reflection of the crown in the pavilion,the arrows are the reflection of the pavilion in the crown at the same time.Through measured samples of a series of diamonds with arrows and hearts effect,it is found that the strict symmetry of cut is not only required,but also the precise proportion is needed.That is to say,the table size should be in the range of 55%~57%,the crown angles in the range of 34°~35°,the pavilion angles in the range of 40°~42°,and the pavilion depth in the range of 43%~44%.