This paper introduces the design, analysis and experimental verification of focal spot X-ray in-line imaging system. First of all, the object transmission function is fixed by the refractive index decrement and the absorption index of tissue according to the previously selected energy. After the factors being analyzed, such as the distance between the object and detector, and the object edge width, which can affect imaging quality, methods presented to improve image resolution are validated. In the experiment, plastic set square is irradiated with X-ray phase-contrast technique. The result is then compared with that using traditional X-ray imaging technique. The experimental results exhibit considerable consistency with former numerical simulation, which proves that the particular method can be used to determine the parameters of imaging system.