To correctly reconstruct the source wavefield in the backward process, it is necessary to extend the boundary and save the boundaries value in a forward process. For 2D-RTM, there are 4 boundaries to deal with. Dussaud [1] et al. proposed saving half-order length of all the 4 boundaries with absorbing boundary condition. In this case, the reconstruction source wavefield is definitely perfect. However, a huge amount of storage is required. In our project, we adopt the scheme proposed by Liu [2] which saved only half-order length of the upper boundaries’ values with absorbing boundary conditions and used random boundary condition for the other three boundaries in order to balance the accuracy and storage requirement.