Gadamer had expressed his idea of practical hermeneutics by the concept of “Solidaritt”. As its core concept, Gadaer discussed etymology sources of “Solidaritat”, and then analyzed its inner three aspects meaning, as well as the theoretical meaning and realistic meaning for the concept of “Solidaritt”.Then, it good for us to grasp gadamer's practical philosophy fundamentally, and understan the gadamer's thought of practical hermeneutics clearly through the concept of “Solidaritt” as its clue.