In this paper, we propose the use of the graphics processing units (GPUs) for acceleration of solution of the H-polarized electromagnetic waves scattering by strip gratings. The approach combines the boundary integral equation method with the Nystrom-type discretization of singular integral equations and is realized with the use of C++ and OpenCL. The elements of the matrix of the resulting system of equations can be calculated independently and, thus, in parallel. The calculation time of the proposed parallelized algorithm on GPU is compared to standard serial algorithm executed on CPU. We considered gratings of graphene strips in vacuum and inside a dielectric slab. The acceleration is up to 35–55 times for the gratings in vacuum and up to 80–140 times for the gratings of 5–20 strips inside the dielectric slab.