Abstract: Body color is an unique phenotypic trait of fish, which is of great significance to the survival of species, avoiding enemy damage and preventing ultraviolet erosion. Coral reef fishes have rich species diversity and body color variation. Plectropomus leopardus, a coral reef fish, shows significantly different body colors in different environments. Its body color is gorgeous and bright, with high ornamental value and high economic value. Plectropomus leopardus is a valuable material to study the development and variation of body color. In order to reveal the mechanism of fish body color variation, Plectropomus leopardus individuals with different colors were selected. The skin color, types of pigment cells and movement state of pigment cells in different parts were observed by means of paraffin section, frozen section and stereoscopic microscope to compare the red and black Plectropomus leopardus. Then, the skin sections of the individuals with different colors were observed to analyze the influence of the number and distribution of pigment cells on the change of body color. Meanwhile, the difference of pigment cells between stress and non-stress groups was also studied. The results showed that the morphology of melanocytes and erythrocytes was mainly dendritic, and some are punctate. The size of melanocytes was 20—35 μm, and that of erythrocytes was 20—25 μm. In the black individuals, the back epidermis were mainly melanocytes, and the cells were zonal distribution. In the abdomen epidermis of the black individuals, a large number of melanocytes were observed. While in the tail of the black individuals, a large number of melanocytes were mainly distributed, the cell density was the largest, some cells were stacked distribution, and the tissue color was the deepest. In the red individuals, the dorsal epidermis was mainly composed of red pigment cells. In the abdominal epidermis, only red pigment cells were observed, with a small number of cells scattered in the tissues and the lightest color. In the tail of the red individuals, red pigment cells were widely distributed, with a block distribution, and a small number of melanocytes were observed in the tail epidermis. In the stress group, body color changed quickly and the granular pigment cells were smaller and darker than those in non-stress group, which was mainly due to the rapid expansion and contraction of pigment cells. This research will lay the foundation for further discovery of the development mechanism of body color formation of Plectropomus leopardus, and also provide theoretical guidance for the breeding.