To characterize the nonlinear mechanical behavior of plain-Braided composites under low-velocity impact, a nonlinear constitutive model based on single-layer modification is proposed. This model innovatively combines a damage-based failure model with a single-parameter plasticity model, achieving decoupled analysis of effective stress and equivalent plastic strain through experiments, thereby separately characterizing material plastic deformation and progressive damage effects. Mechanical property tests on basalt plain-Braided fabric (BPW) laminates were conducted to obtain key parameters such as elastic modulus, strength, and intra-/inter-laminar fracture energy. Off-axis and Iosipescu tests were systematically employed to reveal their nonlinear mechanical behavior. Based on the Sun-Chen single-parameter plastic potential framework, an effective stress-strain relationship model was established and numerically implemented via the ABAQUS/VUMAT subroutine. The results demonstrate that the model accurately predicts the dynamic response of laminates under low-velocity impact, including impact force-displacement curves and energy absorption characteristics. The simulated indentation depth and diameter show good agreement with experimental data, validating the model"s accuracy in analyzing damage evolution mechanisms.