In this paper, ten secondary indicators are selected from three aspects: basic ability, primary knowledge service ability and advanced knowledge service ability. Then, the index weights of these indicators are determined by analytic hierarchy process. According to the intelligence level of intelligent voice assistant at present stage, the corresponding test questions are selected for each secondary indicator, and the evaluation system of knowledge service ability of intelligent voice assistant is constructed. Finally, three mainstream intelligent voice assistants are evaluated and analyzed by this evaluation system. The evaluation index system constructed in this paper is practical and dynamic, the weight of basic ability is the largest, followed by primary knowledge service ability and advanced knowledge service ability. The empirical results show that the mainstream Chinese intelligent voice assistant has certain degree of knowledge service ability at now, but there is still much room for improvement.