As web services are getting wider deployment, Web Services transaction processing(WSTP) are getting more and more attentions. There is a strong requirement for searching a new formal model to describe and reason about WSTP. This paper reports one of the results of the work that examine the WST from the perspective of intelligent agents, which aims to enable WSTP by agents over heterogeneous platforms that can negotiate to initiate and perform WSTP by coordination. Based on the investigation of existing WSTP models, an agent-based WSTP model(AWM) is proposed which covers most of the features but is more abstract and generic. An WSTP implementation model is proposed based on AWM. We believe that the AWM model and implementation model contributes to the design and development WSTP using agents, and can integrate WSTP which use different protocols on heterogeneous platforms.