In this paper we use cellular automata approach to model scanning electrochemical microscopy (SECM) experiments. We simulate SECM current vs distance curve for a negative feedback mode. It shows the effect of the deformation of the diffusion layer around the UME tip close to the substrate surface. We also simulate an experiment where the UME serves to locally dissolve an electrochemically inhomogeneous substrate as a consequence the substrate's geometry changes during the experiment. Our approach gives both quantitative and qualitative information on the simulated experiments. We show that simulations of real three dimensional experiments are already feasible on relatively cheap multigraphical processor unit (GPU) cards in a standard desktop workstation.