Micro channel plate (MCP) used in X-ray focusing and imaging has such advantages as larger field of view, lower weight, and lower sensitivity to device alignment. Based on the X- ray total reflection theory, the focusing properties of flat circular-channel capillary arrays are discussed, and the theoretical calculation of the relative gain and point spread function (PSF) on focal plane against the parameters of MCP is presented. The calculated results are verified via TracePro software, through which the focusing performance of MCP with 25 μm circular-channel diameter is simulated. Both of the model calculation and the simulation suggest that the relative gain of the MCP is nearly proportional to the source distance ls, while independent on the maximum aperture of the MCP. When the source distance is 110 mm, the relative gain can reach about 18. Furthermore, the performance of MCP with misalignment of off-axis and tilt is discussed, which suggests that the off-axis of MCP barely influence the focal spot while the tilts influence the location and shape of the spot.