The study presents the results of the design, simulation, and adjustment of middle-aged men’s Ao Dai from 30 to 60 years old in Ho Chi Minh City. This research combines two methods of 2D design on the Gerber software and 3D design on the CLO3D software, of which the main simulated patterns’ material is cotton sateen fabric. An avatar is used to simulate men’s Ao Dai which has the average measurements of the 378 measurement samples. There are three steps to simulate and edit. At first, the patterns are draped on the avatar. The sample does not achieve a smooth, flat fit in the side seam and waist area when they drape on the avatar. After patterns are adjusted at the side seam, finally, these patterns are draped again to meet the standard of smooth and flat appearance on the simulated model’s front, back, and side faces. The study was conducted on one model that has suitable dimensions for Vietnamese men, so there will be additional avatar data in the CLO3D software database. This is very useful for fashion and technique designers in garment businesses.