The complicated electromagnetic couplings between nanostructures present substantial challenges in the design and simulation of metasurfaces, especially large-scale elements. The couplings are typically neglected in a conventional simulation. We introduce a computational framework that includes the electromagnetic coupling effects between meta-atoms. Decomposing the incident field and segmenting the computing range for individual local simulations allows for an effective and accurate simulation of the entire metasurface. Numerical examples of a 2 mm diameter cylindrical metalens with a numerical aperture of 0.9 and a 1 mm aperiodic beam splitter show the deviation from the conventional method is reduced by 97% compared to the rigorous method, while the computation times are 10 times and 4 times faster than the rigorous methods, respectively.