Abstract: Missile radome is a device for protecting the antenna system from influence of outside airflow when missile is flying with high speed. But the radome itself will produce some inverse effect on the property of antenna indeed, and the far directional pattern of radome could be used to assess the affect of the property by means of a numerical method. Based on the plane wave spectrum surface integration method, the electric property of the radome is analyzed and the method how to determine the integral area for numerical calculation of the pattern is presented in the paper.