In the present study, a numerical methodology of the heat transfer analysis of a plate heat exchanger is investigated. An analysis method for the conjugate heat transfer between the repeating set of a cold flow passage, separating plates, and a hot flow passage of a plate heat exchanger is proposed and successfully performed by using the periodic boundary condition at the center area of the plate and appropriate inlet and outlet conditions for the two streams. Comparison of the heat transfer results of the proposed analysis method with the available experimental data showed a good agreement.