An in-situ coin cell support device for transmission mode X-ray diffraction analysis capable of controlling temperature. The device includes a coin cell seating unit including a seating part for receiving an in-situ coin cell, a positive electrode tab coupled to the seating part and connected to a positive electrode of the in-situ coin cell, and a negative electrode tab coupled to the seating part and connected to a negative electrode of the in-situ coin cell, a housing having a heat-insulating function, which surrounds the coin cell seating unit such that the positive and negative electrode tabs extend outwards from the housing and which includes one side wall and an opposite side wall arranged opposite each other with the in-situ coin cell interposed therebetween, and a temperature control unit coupled to the exterior of the housing and including an inlet port, an outlet port, and a flow passage.