The Geant4 program was used to simulate the effect of micropore shape on the performance of CsI:Tl X-ray scintillation screen based on silicon microchannel array (SMA). The simulated scintillation screen performance parameters include: scintillation photons, bottom light output, transmission efficiency, percentage of n times total reflection, and modulation transfer function (MTF) versus spatial resolution. The shapes of the micropores were set to be square and circular during the simulation process, and the microchannel array period was the same for both hole shapes, which was 10 μm. The simulation results show that the number of scintillation photons in square micropores is better than that in circular micropores, and the number of fluorescent photons is directly proportional to the cross-sectional area of the micropores; while the thickness is less than 400 μm, the bottom light output of square micropores is better than that of circular micropores, when the thickness is greater than 400 μm, the situation is opposite; The transmission efficiency of circular micropores is better than that of square micropores; For the thickness of 40 and 200 μm, the spatial resolution of the square micropores scintillation screen is better than that of the circular micropores scintillation screen with the same thickness. A square microporous CsI: Tl scintillation screen sample was prepared, and the relationship between its MTF and spatial resolution was measured. When the MTF was 0.1, the spatial resolution was 22.6 lp/mm.