The pulse-dilation framing camera, with a short magnetic focus, is a two-dimensional, ultrafast diagnostic device with a long drift region. It evaluates the paraxial spatial resolution and detection area by the point spatial resolution of the on-axis and off-axis, respectively. However, because of the spatial nonuniformity of the Gaussian image plane caused by the field curvature, the overall spatial resolution of the camera is difficult to evaluate. Therefore, this study proposes a new method to quantify the spatial resolution of a pulse-dilation framing camera. The proposed method is based on a model constructed using the COMSOL software. In this model, the three-dimensional imaging surface is reconstructed based on the characteristics of the field curvature. The degree of deviation between the imaging surface and the Gaussian image plane is analyzed by standard deviation (SD), and the spatial resolution of the Gaussian image plane is obtained by combining the point spatial resolution and the overall modulation. The spatial resolution uniformity of the Gaussian image plane is quantified using relative error. The results of our study show that, when the lens aperture is 200 mm, slit width is 10 mm, axial width is 100 mm, length of drift region is 400 mm, imaging radius is 21 mm, and the cathode voltage is -3.75 kV, with the change in magnetic field, the degree of deviation between the imaging surface and the Gaussian image plane, and the spatial resolution of the Gaussian image plane both have an upward parabolic shape. When the imaging magnetic field is 41.97 Gs (1 Gs=10^-4 T), the SD of the deviation of the two image planes is minimized to 2.82 mm, the spatial resolution of the Gaussian image plane is optimal at 292.80 m, and the modulation difference characterizing the spatial uniformity is minimized to 330%. In conclusion, this study proposes a quantifiable reference method for evaluating the optimal spatial resolution performance of a pulse-dilation framing camera with a short magnetic focus.