In this paper the effect of electromagnetic field lengths to change simultaneously is simulated on the temperature distribution and flow velocity of a MHD micropump considering the lateral electromagnetic diffusive regions. The geometry of flow is a two-dimensional channel between two parallel plates and the flow is assumed to be incompressible, steady and laminar. In addition, thermophysical properties such as the dynamic viscosity and electric conductivity of fluid are considered to be the function of temperature. The governing equations of both flow and electromagnetic fields have been solved using the finite volume numerical method a comprehensive analytical solution including velocity, pressure and temperature filed distributions has been derived for an special case. The numerical results show that by changing the length of electromagnetic fields and considering the fluid (water) properties as a function of temperature, for flow in a 1000 mm2 cross-section channel, magnetic field intensity 0.025 Tesla and electric field strength 20 volt/mm, the flow rate reaches 250 mLit/s and the mean cup temperature from 25 0C at entrance reaches to 40 0C at the exit of channel. However for constant properties, the flow rate and the mean cup temperature reach 70 mLit/s and more than 60 0C respectively.