A single discharge temperature field simulation in micro electrical discharge machining (micro EDM) using finite element method is introduced, which mainly influences the materials removal of electrodes. With given process parameters, the materials removal amount of both tool electrode and work piece in single discharge were calculated considering heat source model, energy distribution and boundary conditions. The influences of process parameters on the material removal amount of anode and cathode respectively have been researched and discussed under the analysis of simulation results. Results show that the discharge current has more degree of influence on material removal amount than the discharge on-time is. Meanwhile, with the discharge current increases, the difference of material removal amount between anode and cathode in micro EDM enlarges. From the simulation results, it is interestingly found that the influences of material removal amount against discharge on-time are not the same as the discharge current. With the discharge on-time increases, the material removal amount of both the electrodes increases, but the difference of the removal amount between the anode and cathode has a maximum value at the discharge on-time of 8µs. The simulation results are helpful to select machining parameters in the discharge experiments for good machining performance.