The magnetically focused pulse-dilation framing image converter tube is an ultrafast diagnosis device with a temporal resolution within 10 ps and a spatial resolution that closely relates to the imaging magnetic field. In this study, a model of a pulse-dilation framing image converter tube was constructed and the spatial resolution of the point imaging distribution was calculated under the Rayleigh criterion. The imaging magnetic field was applied with emission areas of different radii, and the imaging magnetic field was optimized by finding the optimal on-axis and minimum difference between object points. In the pulse-dilation framing image converter tube with a magnetic lens, the overall spatial resolution was not improved by increasing or decreasing the magnetic field, but was optimized by the magnetic field of the specific emission area. When the lens aperture is 160 mm, the slit width is 4 mm, the axial width is 100 mm, the drift area is 500 mm, and the emission energy is 3 keV, the imaging magnetic field is optimized by setting the emission area radius to 8 mm and the maximum magnetic field along the axis to 37.87 × 10^-4 Tesla. As the spatial resolution of the microchannel plate is 55 μm and the imaging is 1∶2, the spatial resolutions are 29.86 μm, 43.08 μm, 87.07 μm, and 276.88 μm at locations of 0 mm, 5 mm, 10 mm, and 15 mm on the object plane, respectively. The simulation results are consistent with the measured data. This work provides a reference method for establishing the relationship between the imaging magnetic field and overall spatial resolution and for optimizing the calculations of the spatial resolution simulation.