The recent development of cross-border e-commerce has changed drastically as the consumers’ consumption habits continues to expand the online market. This study aims to discuss the development of cross-border e-commerce market and strengthen international trading with Taiwan’s New Southbound Policy and to explore the key success factors (KSF) for the development of cross border e-commerce platforms and prioritize Southeast Asian countries to expand the market. Based on literature reviews and expert opinions, this study develops a diagrammatic representation of how the research should be conducted in the following order: BOCR (Benefits, Opportunities, Costs, Risks) four dimensions, fifteen assessment criteria and three counties (Philippines, Vietnam, Indonesia) of selection. Then, conduct a questionnaire with analytic hierarchy process (AHP) methodology. Results showed that “opportunities” is the most important dimension among BOCR four dimensions from overall perspective, followed respectively by “risks, benefits, and costs”. In the assessment criteria, “localization” and “regulations” are the most important KSF for cross-border e-commerce. Regarding the expansion of Southeast Asian countries, overall assessment suggests “Vietnam” as the primary development market of cross-border e-commerce. However, the results of “cross-border trading business” cluster assessment points out “Indonesia” as the primary market for development. The result of this study can provide as a strategic reference for leading e- commerce platform companies to expand its market abroad in Southeast Asia.