The spatial distribution of the energy deposition in polymer resist PMMAby lateral tcattering electrons is simulated with Monte Carlo method. The combination of the scattering mean free path and the constant step value is proposed, for making a compromise between the physics concept and the computer runtime.A new approch that whether or not an elastic scattering event occurs on the boundary is determined by a randum number is utilized. The graphs of both forward scattering energy deposition and backward energy deposition have been given in the present paper.