As trend toward liberalization, telecom industry in Taiwan is getting more and more saturated. It means that competition between telecoms firms is getting more and more sharp. As a result, all telecoms firms are striving to gain and keep their customers and trying so hard to understand comsumer behavior on choosing telecoms firms. In the past, researches on consumer behavior are usually base on quantitative methodology. Quantitative researches on consumer behavior focused on specific moment of customers. This research is base on qualitative methodology to extend consumer behavior on choosing telecoms firm from a specific moment to a dynamic model and establishing a thorough consumer behavior on choosing telecoms firm model. This research on consumer behavior on choosing telecoms firm is base on grounded theory. By the analysis and coding process of the interview data that collected from eighteen interviewers in a theorical sampling process, this research generalizes eighty three open coding and fifteen axial coding. In the selective coding process, this research generalize three major concepts of consumer behavior on choosing telecoms firm and establishes a model of consumer behavior on choosing telecoms firm.