A large cathode framing tube was designed and developed based on the pulse-dilation technique. By virtue of Matlab programming, the spatial resolution of off-axis positions and the imaging distortion for magnetic double-lens and single-lens imaging were numerically simulated respectively. Resolution plates photoetched on the cathode micro-stripe were adopted to test the spatial performance of the tube. The experimental results show that at an imaging magnification of 2:1, the spatial resolution of the positions within 9 mm from the centre is higher than 5 lp/mm. Compared to magnetic single-lens imaging, the magnetic double-lens tube possesses a higher spatial resolution, a wider imaging range and a lower distortion, which provides a new way to improve the spatial resolving power of framing image converter tube.