Abstract: The film that its mass thickness was measured by α-particle energy loss(method) was regarded as constitute of many layers.Each layer thickness was calculated.The total film thickness was obtained by summing thickness of every layer.It is shown that this dividing layer computing method can increase the measurement accuracy by 30% for α-particles from ~(241)Am.It is also seen that the sensitivity of thickness measurement with α-particle can be improved by lowering appropriately the energy of α-particle.