This study is an attemptive one on the responder’s provision of additional information i.e. responder’s overinformativeness (RO), in the institutional discourse—TV interview, seeking to explain the adaptability of this phenomenon. Concerning this issue questions being explored include what manipulations and functions of overinformativeness are manifested and how overinformativeness adapts to contextual factors such as politeness (including power), identity construction in the course of interview. This study is mainly based on qualitative analysis of the data, which is in fact the pragmatic interpretation of the answer to the questions. Based upon Verschueren’s theory of linguistic adaptation, the author endeavors to construct a theoretical framework as to the functioning mechanism of responder’s overinformativeness and to analyze how the adaptation regarding politeness and power takes place in overinformativeness. The responder’s overinformativeness is variable along a few dimensions, interactional component (direct self-oriented or indirect other-oriented), contextual component (retrospective or present or prospective) and the propositional component (mono-propositional or multi-propositional). As regards the functions of responder’s overinformativeness, micro-level functions and macro-level functions are discussed. For the micro-level functions, the analyses are launched from two aspects, how RO contributes to the discursive identity construction and how RO helps construct an ideal identity and a retrospective identity. The former is the focus of our analysis where we illustrate it from three angles: enhancing positive self-image, enhancing negative other-image and strengthening the forcefulness of the talk. With regard to the macro-functions, RO can maintain the ongoing talk such as avoiding the confrontation of interactants and mitigating the embarrassment and face-threat;RO can prompt the ongoing discourse by conveying good self-image and introducing a new topic-center shift. The adaptation in the overinformativeness to the contextual factors including politeness and identity construction is another main part of this paper. For the sake of clarity, the adaptation of RO to the three worlds is summarized into two categories: self-oriented and other-oriented. The former concerns the adaptation to social variables related to the responder’s motivations (identity construction), emotions and social politeness (including power). The latter involves the adaptation to other presences in the speech situations related to the topic of talk and the questioner’s expectation.