Abstract: Seventeen plain groups, which were associated with 2D braided geometry of composites, were deduced from the combination of ten plain point groups and five plain dot lattices. The simplified method, combination and crossover principle of the point symbol on a 2D braided composites yarn segment were proposed. The construction methods of non-symmetry unit and basic symmetry unit were investigated, and the fabric-braided procedure from non-symmetry unit to basic symmetry unit was discussed. The 2D braided fabric of composites was classified four braided families, each braided family included several plain groups, each plain group was corresponding a group of braided structures, and each group of braided structures had one or several braided modes whose interwoven methods were homologous. The possible 2D braided composites geometry of majority plain groups was illustrated.