In this paper, a hybrid method is proposed to analyze the electrically large radome covered Cassegrain antenna at millimeter wave band. The reflector antenna is analyzed by the physical optics and the electrically large radome is modeled by the hybrid physical optics-boundary integral-finite element method. With this hybrid method, the antenna-radome system can be analyzed more exactly and more efficiently. The antenna and the radome at 94 GHz are designed and tested. The predicted radiation pattern has acceptable agreements with the experimental results.