The draping and buckling of knitted fabric is simulated based on the micro-mechanical constitutive model with full Lagrange finite element method under gravity load. The micro-constitutive model reveals the mechanical properties of fabric more elaborately, especially fabric has its own properties owing to its micro-knitted structure. In the finite element analysis, the knitted fabric sheet is discretized with 8-node shell elements and reduced-integration method is used. The simulated results are in good agreement with the experimental observations. The work provides a theoretical and technical basis for the development of the virtual trial system of garments.