This work illustrates the setup and solution of a three-dimensional turbulent fluid flow and heat transfer problem in a mixing poly flow pipe junction by fluent under ansys 12 (finite volume). The mixing poly flow of water configuration is encountered in piping systems in power plants and process industries. It is often important to predict the flow field and temperature field in the area of the mixing region in order to properly design the junction. In this work a different Reynolds number are used to predict the better mixing in poly flow pipe. Coarse mesh type are available for more accurate and the inlet velocity and temperature of the fluid can be specified and the effect of the side stream on mixing within the poly flow pipe can be observed. Temperature dependent fluid density, viscosity, thermal conductivity, and specific heat can be specified. Pressure drop and temperature change from Inlets to the Outlet are reported. Plots of velocity distribution, pressure distribution, temperature distribution, are available also velocity vectors, temperature contours, and streamlines can be displayed in the flow domain