In this paper, we present the body of knowledge which is transferred between client and vendor in ISD (Information System Development) offshoring outsourcing project, which are domain knowledge, technical knowledge, process knowledge and culture knowledge We also find the process of knowledge transfer though the whole ISD project life circles by case study. The results showed that in different stage of project life-circle, lite transfer intensity of every kinds of knowledge are different. Domain and business process knowledge are what vendors lack of most according to the current situation of knowledge base for vendors in China. They can accumulate lots of know-how through cooperation with clients in western markets from different vertical industry. We also proposed key factors impacting the effectiveness and efficiency of knowledge transfer in real-life ISD offshoring outsourcing project, which are project character(novelty customization, complex),client character(firm size, interaction participation, process maturity),client-vendor related character(communication quality, knowledge overlaps, prior cooperation experiences) and vendor character(firm size, work dispersion, absorb ability,culture fit). Among those factors, most of the respondents emphasis that communication understanding and culture fit are what they most concern of knowledge transfer in onsite-offshoring/dispersed setup. The managerial implications derived from our knowledge transfer framework may help guide vendors pay more attention on the training of culture and communication skills for the employee, And vendors should design knowledge management systems or implement CMM or CMMi to acquire know-how as much as they can through every project.