Heat dissipation capability of an electronic system has become one of primary limiting factors for circuit miniaturization. Effective cooling of electronic components is crucial in maintaining the circuit normal operation and enhancing reliability. Numerical simulation is performed for flow field and temperature distribution of rectangular enclosure in which there is a five chips horizontal substrate on the bottom by using finite volume approach . The result shows that the position of the arrangement of electronic component affects strongly the temperature distribution of the environment around circuit board. The conventional equispaced arrangement is not an optimum option. Non - equi -spaced arrangement can reduce effectively the thermalload of electronic component. An optimum arrangement position should be selected when designing circuit board.