Laminar free convection heat transfer of non-Newtonian power law fluids over a vertical flat plate has been studied.It is a problem of nonlinear two point boundary values.The two-system of partial differential equations for velocity and temperature are coupled and nonlinear. Three numerical methods are also used to calculate the problem.The effects of Prandtl numbers(Pr) and various flow indexes on convection heat transfer(Nu) have been discussed and the calculations are compared with each other and with the results of other papers.