VoIP (voice over IP) traffic generation has significant meaning for the measurement of VoIP quality in networks, but existing generation methods are insufficient both in reality and interactivity, and thus affect the accuracy of VoIP quality measurement. This paper proposes a conversational model based VoIP traffic generation algorithm, which simulates the behavior of two users in a VoIP session, and generates VoIP traffic for the quality measurement according to the specific voice codec and VAD (Voice Activity Detection) parameters. Our experiments show that the algorithm illustrated in this paper can effectively demonstrate the influence of conversational users' speech characteristics and interactive process to VoIP traffic, and thus provides more realistic and interactive traffic for practical quality measurement activities.