The lobster eye telescope is promising for large-field x ray imaging in astronomy. The special structure of the lobster eye system makes the focal plane a sphere, resulting in detector defocus when the field is large. In this study, we established a model based on the principle of lobster eye imaging and simulated the imaging at different image distances. The results reveal the relationship between the defocus and position accuracy and angular resolution. To ensure the optical performance of the large field lobster eye telescope, we propose a detection system design method using multiple detectors stitched together to form a spherical-like surface and apply it to the development of the Einstein Probe/wide-field x ray telescope (EP/WXT) submodule. About 70% of the detection area is out of focus within 0.5 mm. The scanning image of the integrated WXT submodule shows good uniformity of the point spread function (PSF) for various incident angles, and the effect of defocus on imaging is acceptable.