To solve the problem of ultra-low stray light in highly sensitive refractive optical systems and super narrow spectrum detection systems， the theory of ghost images formed by the focal plane is used. First， according to the characteristic parameters of the photosensitive surface， the theory of ghost images formed by the lens and focal plane was proposed. Subsequently， the Light-tools software was used for modeling and analysis. The principle， position， and energy relationship between the ghost points and the image were calculated and simulated. Finally， a series of ghost image experiments were designed and carried out to validate the accuracy of the data. The simulations and experiments indicated that the ghost image and the original image were isometric， confocal， and centrosymmetric. The results showed good agreement between the conclusions of the simulations and experiments. Thus， the validity and rationality behind the formation of ghost images were proved. The results can be used as a guide for the design of other refractive optical systems.