An attitude angle measuring system based on photoelectric collimation and virtual extension imaging is established to enlarge field of view (FOV) of system. The FOV is virtually enlarged through multi-imaging. The main principles of system is introduced, and error sources which may affect measuring precision of system are analyzed based on system model. Experiments on error sources and system measuring precision is simulated under their mathematic relations. Simulation result is used to analyze and verify the system design. The results show that the proposed factors indeed affect system measuring precision. Based on the results, approaches to reduce system error and improve precision can be proposed.