Abstract: The eight hearts and eight arrows effect of diamond has been accepted by the majority of consumers, but its formation reason is complex and lack of relevant literature, which causes different opinions on the Internet.This paper mainly uses GemCad, a Gemstone drawing software, and DiamCalc, a simulation software, to simulate the optical effects of real diamonds and verify the accuracy of the simulated optical effects through physical diamond photography. Using the drawing of different shapes and the simulation of the optical effects of the drawn shapes, the images of the eight hearts and eight arrows of the diamonds are deconstructed to explain the formation of the eight hearts and eight arrows effect of diamond. The results show that the cause of the formation of the eight hearts and eight arrows is different from that put forward by predecessors. In particular, the formation of the hearts is not the reflection of the main facets of the crown mentioned by predecessors, but the reflection combination of the main facets of the pavilion. In addition, the influence of different facets on the hearts and arrows is also different, all of which is explained in this paper. The method proposed in this paper that uses GemCad and DiamCalc to model and simulate the optical effects of diamonds, also has some reference significance in the field of design of eight hearts and eight arrows diamonds.