A purpose of this study is to do fundamental research of construction of coat patterns in the Daehan Empire in order to make replicas of the costumes. This study is composed of literature research, investigation of artifacts, and experiment of pattern making. The results of this study are as follows. First, even if the 15th Court Dress Rules regulated color, fabric, number of flower, width of braid, and size of button, there was no regulation regarding the shape of the coat. The analysis of the photos in those periods shows that the style of the tailcoat was different from that of today in the length of the front, the shape of breast and collar. Second, six artifacts in the collection showed that the shoulder line and the sideline were located on the further rear side than the current tailcoat. This can be confirmed in the western and Japanese pattern book, and especially the pattern drafting method in the books published in Japan in 1900s is different from current one in setting base lines of front bodice and back bodice. As a result, based on several experiments, this study proposes how to make coat patterns. The shoulder line, the sideline, and the princess line should be located in the back of the dress similar to the shape of swallowtail coats of 1900s. The front bodice should be constructed without the composition line in order to add embroidery on it. The collar, which shape looks like long half moon, should form V-shape neckline in the front breast when adjusting dress. The sleeves should be constructed top and down, and it should curve more than the modern design.