We propose a two-dimensional (2D) multiparticle Lorentz gas model by combining the direct simulation Monte Carlo method with the Lorentz gas model, where the normal thermal transport under Fourier's law is confirmed by length-independent thermal conductivity. For this 2D multiparticle Lorentz gas model, the thermal rectification effect is obtained with the asymmetrical setup of a trapezoidal shape, which is a purely geometric effect. Furthermore, we find a scaling behavior between the rectification ratio and the geometrical parameters of the trapezoidal shape, which is verified by numerical simulations.