Molecular Dynamics(MD) is a computer simulation of physical movements of atoms and molecules in the context of N-body simulation, and is an important part of pharmaceutical industry. GROMACS, which is the most popular software for MD, could not perform satisfactorily with large-scale for the limit of computing resources. In this paper, we proposed a method to accelerate GROMACS with offload mode. In this mode, GROMACS could be arranged efficiently with CPU and the Intel® Xeon PhiTM Many Integrated Core (MIC) coprocessors at the same time, making the full use of Tianhe-2 supercomputer resources. To promote the efficiency of GROMACS, we proposed a series of methods, such as synchronization, data reassemble and array reuse. As we known, we are the first to accelerate GROMACS in offload mode on MIC.