Thermal stress induced by the mismatch of the thermal expansion coefficients between dissimilar materials becomes an important issue in many bi-layered systems, such as composites and micro-electronic devices. It is useful to provide a simple and efficient analytical model, so that the stress level in the layers can be accurately estimated. Basing on the Bernoulli beam theory, a simple but accurate analytical formulation is proposed to evaluate the thermal stresses in a bi-material beam. The analytical results are compared with finite element results. Good agreement demonstrates that the proposed approach is able to provide an efficient way for the calculation of the thermal stresses. It is shown that thermal stresses are linear proportion to the ratio of thermal expansion coefficients between the two materials. Parametric studies reveal that thermal stresses in each layer are decreasing with the increase of thickness, and are increasing with the increase of Young’s modulus ratio between the two materials.