This paper presents a simulation based analysis method for service diffusion in consumer networks. Services with good qualities do not always diffuse because service quality is often unstable because of the nature of service delivery systems involving human. Consumers cannot also confirm the quality of service before purchase because service has no shape. Therefore, it is necessary to study diffusion process of service by computer simulations to clarify the process of acceptance among consumers in consideration with heterogeneity of consumer utility due to the unstable service quality. This paper proposes a multiagent-based model for diffusion of plural competing services repeated purchased in consumer networks including heterogeneity of consumer utility. It is verified that the heterogeneity of consumer utility and network structure affect service diffusion process in the results of computer simulations. Finally, the diffusion process of services is concluded in terms both of the number of service and repetition of service purchase.