This research aims to study Yun Hyu's Simui system as described in the Simuijego(深衣制考) within Dokseogi(讀書記) Doksangbokjeon(讀喪服傳) of Japjeo(雜著), Book 42 of Baeghojeonseo(白湖全書). Rather than follow Zhu Xi's Simui system, which was perceived as a canon, Yun Hyu criticised the theoretical and practical problems in Zhu Xi's Simui and presented his own Simui system based on the evidence of traditional practices and his own interpretation to solve them. Yun Hyu's Simui system is characterised by the following features. Yun Hyu's Simui featured an overlap-style Jikryeong Simui with a Seop attached at the top, providing substantial coverage to the upper body. The front bodice and back bodice each measured 2cheok and 4chon in waist width, and the width of the bodice and Seop was 1cheok and 2chon. The garment included two skirts attached to the outer, inner and back bodices of the front bodice, as well as to the Seop. Notably, Yun Hyu's design incorporated overlapping elements in both the bodice and skirts, creating a deeply wrapped lower body. Detailed measurements included a bodice length of 2cheok and 2chon, an armhole width of 1cheok and 4chon, a sleeve width of 2cheok and 2chon, and a sleeve wrist circumference of 1cheok and 2chon, accommodating the comfortable placement of Daedae accessories beneath an armhole. Moreover, Yun Hyu's introduction of round sleeves, which tapered toward an armhole and wrist, marked a significant departure from the traditional garment construction. This study highlights Yun Hyu's Simui as pivotal in the evolution of this traditional Korean garment during the Joseon Dynasty for several reasons. First, it represented a variation on Zhu Xi's Simui, challenging established norms and proposing new interpretations within Joseon Confucianism. Second, Yun Hyu's structural innovations, such as the overlapping bodice and skirt pieces and the introduction of round sleeves, contributed significantly to the development of other traditional attire. Finally, Yun Hyu's Simui exerted a lasting influence on subsequent scholars, notably impacting Lee Ik's (1681-1673) Simui system and facilitating the division of Joseon Simui into Jikryeong Simui and Bangryeong Simui. This study underscores the significance of Yun Hyu's Simui system during the Joseon Dynasty, offering a comprehensive analysis of its historical importance.