RC (Ritchey-Chretien) optical system has hyperboloidal primary and secondary mirrors, and the off-axis field has large astigmatism. The processing and alignment of RC optical system has some particular characteristics. The influence of errors in the processing and alignment of RC optical system need analyzing. The traits in the processing and alignment are evaluated by using interferometer and software Zemax. Comparing the tested wavefront with those simulated results of Zemax, the errors in the processing and alignment of an RC optical system are judged. After proper modifications of the processing errors and misalignments, the optical system meets the requirement of the design finally.