The purpose of this study was to develop slacks patterns for middle-aged abdomen-obese adult males by using the 3D virtual-twin and virtual-garment simulation system. The criteria for subjects in this study were males who had over $25kg/m^2$ of BMI, over 90cm of waist, and over 0.90 of WHR. A total of 211 adult males who met these criteria were enrolled. The results were as follows: first, a new slacks pattern considerate of abdomen-obese men was development. The basic numerical formula were as follows: front and back hip girth H/4+3.5, front waist girth W/4+1+0.5, back waist girth W/4+1-0.5, front crotch extension H/16, back crotch extension H/8-0.5, front pleats amount 2.7, and back dart amount 1.5. Second, according to the results of the new slacks patterns appearance evaluation, the new slacks pattern scored more highly than the existing pattern in silhouette and ease amount, confirming that the new slacks pattern is appropriate for the abdomen-obese men. Also, the new slacks pattern was evaluated allowing proper space length of waist, abdomen and hip. Virtual models of production through data from a 3D body scan, pattern draft and virtual garment digital program were applied to a prototypic design method in order to enhance the fitness of ready-made garments. The use of the virtual twin made it impossible to comprehend the appearances and ease correspondent to motions. In order to evaluate wearing fitness, therefore, the system should be improved so as to change arm positions and perform various motions.