We propose the mesh sharing based method for fast electromagnetic (EM) simulation that involves parameter sweep. The proposed method leverages mesh sharing for the common portion of the designing space, which has to be processed separately from scratch without special solutions. The system matrices resulted from discretizing the governing integral equation for different parameters would have a large proportion of identical elements thanks to mesh sharing. Instead of explicit extraction from the super-matrix, we propose the implicit approach that integrates elegantly into the iterative solver and avoids redundant computation in the meantime. Besides, the proposed method is compatible with the $\boldsymbol{\mathcal{H}}$-matrix framework, which is adopted to accelerate each single round EM simulation. Numerical examples show that our proposed method leads to accurate results for different configurations with single round $\mathcal{H}$-matrix construction, which demonstrates its effectiveness and efficiency for fast parameter sweep and design.