Abstract: In the stiffened plate's meshless model, the ribs' position is critical to the mechanical performance of the stiffened plate under various working conditions. Based on the first-order shear deformation theory and the moving-least square approximation, a meshless model of the stiffened non-rectangular plate considering nonlinearity is proposed and the position of the ribs is optimized based on the genetic algorithm. Firstly, the meshless model of the stiffened plate is obtained by discretizing the plate and ribs with discrete nodes. Secondly, the bending governing equation for the geometrically nonlinear problem of the stiffened non-rectangular plate is derived from the Von Karman large deflection theory. Then, the governing equation for the free vibration problem of the stiffened non-rectangular plate is derived from the Hamilton principle. Finally, the genetic algorithm is introduced with the position of the ribs as the design variable and the minimal deflection or the maximal natural frequency of the center point of the non-rectangular stiffened plate as the objective function to optimize the position of ribs. In the process of ribs' position optimization considering the influence of geometric nonlinearity, only the displacement transformation matrix needs to be recalculated when the ribs' position changed, and the mesh reconstruction is totally avoided.In this paper, first taking the single-rib rhombus plate under global load as an example, the comparison with the theoretical results is carried out and the validity of the method is verified. Then, taking the minimum center point deflection and the maximum natural frequency of the stiffened plate as the optimization objective, the stiffened plates with different shapes and different rib' arrangements under local load were optimized, and then the convergence and stability of the proposed method were studied.