The detecting image simulation for an orbiting camera has played an important role in the feasibility argumentation,the research of information processing method and the test of orbiting optical camera on the ground. In this paper,a relative kinematics model,a catoptric character model,an imaging model of camera,and an imaging model of background stars are established and the digital simulation system for detecting images of an orbital optical camera is designed and realized on the basis of the measurement principle and work environments of space-based optical cameras. Measurement noises and detecting sensitivity are analyzed and the effect of all kinds of disturbing factors on the images are taken into accounts in the simulation modeling. The equivalent calculation from the visible magnitudes of background stars to instrument magnitudes is conducted through the detecting wave band of the camera to improve the fidelity of simulated images (detecting magnitude>9 mV,calculating error<10%). Finally,the simulation software is implemented by means of Visual C++ and OpenGL on the basis of designing simulation flows. The simulation and validation of detecting images is undertaken according to the CCD and optic system parameters of the orbiting optical camera. The conclusion can be drawn that this system provides technical supports for the scheme design and performance test of the camera.